Protected Areas as a Center of Attraction for Visits from World Heritage Cities: Extremadura (Spain)

: Conservation of the environment has become a key factor in tourist development, as is shown by the increase in visitors to natural parks and other places with rich ecosystems. Protected areas have become polarised centers for tourists of very varied characteriztics, not only for those who make them their main destination, but also for those who travel to nearby areas. This situation can be observed in Extremadura, where numerous tourists make the best use of their stay in the main centers of tourist attractions of the region to make local trips and thus get to know the most signiﬁcant natural areas. These movements are being detected in varied aspects of demand, sometimes with little connection between the main and secondary motivation for the trip. We therefore consider a variable percentage of tourists visiting the main cultural destinations of Extremadura who use part of their stay to get to know protected areas. With the aim of structuring the research, we made a systematic study of tourists who spent the night in the cities of C á ceres and M é rida, which are World Heritage sites. During their stay, they visited prestigious natural places such as Monfragüe National Park, the Villuercas–Ibores–Jara Geopark, the Tajo Internacional Nature Reserve, and the Garganta de los Inﬁernos Nature Reserve. This information was obtained by carrying out surveys, which allowed us to determine the attraction capacity of each protected area by applying a network analysis. The results reﬂect a heterogeneous type of visitor who travels to the most appreciated areas following guidelines marked by the time of the year, his / her preferences, and the duration of his / her trip.


Introduction
The recreational use of protected natural spaces has been increasingly important in recent decades, as is corroborated by the increased demand for this type of area for relaxation. This results in the shaping of a considerable flow of tourists from large cities [1]. As a consequence, these spaces have become tourist resources of some relevance, especially in inland areas, and have taken their place among destinations of interest that are in demand in certain periods, during which their capacity of attraction increases sharply [2][3][4].
In the Spanish context, the specific literature in which the role of natural spaces as areas of interest for encouraging socio-economic development began to be considered appeared in the 1980s, when the possibility of these areas becoming spaces for tourism and recreational use began to be explored. This leisure, recreational, and tourist use, which has become more widespread, gave rise to interesting studies devoted to encouraging the planning of visits [5] and to analyzing the importance they acquire Land 2020, 9, 47 2 of 22 as resources for either tourist or recreational use [6,7], and some authors even dealt with the educational role they might play in an ever more urbanized society [8].
Despite the thematic variety of the pioneering studies of the use of this particular type of space by tourists, there has been a strong trend of marketing these areas, especially during this century. In many cases, this occurs under the premise of the need for their sustainable use in line with the course of action initiated some decades previously [9]. Numerous studies thus arose to touch on aspects of sustainability in one way or another. Studies which aim to measure the carrying capacity that can be withstood by the area in question thus stand out [10,11], and at the same time new phenomena linked to the process of naturbanization [12,13] or determining their capacity for attracting people [14] are examined in greater detail.
Interest in using protected areas as tourist spaces is growing, as they are becoming more attractive to visitors. Indeed, if we take Spanish national parks as a reference, there was a significant increase in the number of visitors, from 11,559,585 in 2013 to 15,439,502 in 2017 [15]. This important growth justifies the need for a specific analysis of these areas as differentiated tourist spaces, which goes further than considering them as places which bring together privileged ecosystems that need protection and specific management [16][17][18].
The use of protected areas as resources oriented towards ecotourism has been treated thoroughly in the bibliography. Some studies concentrate on the growing number of protected areas on a world scale and at the same time stress the increase in tourists attracted to them, which serves as a basis for drawing up management models capable of minimising the impact of the influx of visitors [19]. Means of reducing this impact include controlling the number of visitors, modifying their behavior, or even adapting the resource to new forms of exploitation [18].
Although it is true that a profusion of analytical studies referring to varied aspects of protected natural places can be found in the literature, it is no less true that there are deficiencies in specific themes, such as measuring their capacity of attraction for either tourists or daytrippers. Indeed, there are major gaps in the research on tourism in these areas, such as the impact it causes, the management carried out in them, or other aspects of a predominantly tourist nature such as visitor satisfaction [20]. This reveals that these areas need specific governance models [21] which compatibilize the protection of existing ecosystems and their tourist exploitation in such a way as to encourage sustainability [22,23] by means of suitable tourist policies [24][25][26]. In essence, what is pursued is encouragement of the green economy from these places [27] by offering solutions based on nature itself in order to achieve sustainable development [28].
It is clear from the literature that protected areas have evolved from being characterized by having unusual and well-preserved biotopes and biocenoses to becoming tourist spaces which are intensely exploited at certain times of the year, so they need a differentiated analysis that goes beyond a study of their components. To do so requires placing faith in the development of sustainable tourism [29] designed to preserve resources, but also to maintain the population of rural areas and obtain economic benefit which contributes to the maintenance and management of these areas.
Although numerous studies refer to protected natural areas as increasingly popular tourist areas and insist upon the need to develop governance models which aim to improve their sustainable management, these areas are not usually analyzed comprehensively. To a large extent, in fact, tourist activities have arisen spontaneously and even today continue to lack well-organized development models. For this reason, it sometimes appears that tourist destinations are created spontaneously and encourage the attraction of visitors without taking into account their impact.
It can be observed in this sense that although it is true that more knowledge of these areas is being acquired from an environmental point of view, the same cannot be said of their exploitation as tourist spots. Despite this, in recent years there has been more interest in getting to know the visiting patterns of these spaces, ascertaining where the visitors come from, their reasons for visiting, or other significant peculiarities obtained by means of direct surveys or Big Data [30][31][32]. However, there are extremely few studies which measure their capacity to attract visitors who are on holiday in the vicinity. As a result, despite the fact that information on the origins of visitors is more readily available, it is necessary to undertake a study to determine how far their areas of influence extend and which travel routes visitors use. Some authors have made affirmations in this sense, although when references are made to this effect, they are generally from the perspective of governance and management models for specific natural spaces [33,34] or overall ones on a national level [35]. Nevertheless, gradually some analyses are being carried out which emphasise mobility as a key factor in facilitating the management of tourist destinations [36,37].
This type of study stresses the need for familiarity with the capacity for attracting visitors to protected areas, as they can be used as tourist resources for practising certain forms of tourism, as occurs generically with ecotourism [38,39] or specifically with ornithological tourism [40]. It also reveals the opportunity to measure their capacity of attraction, not only for tourists who make them the final destination for their holiday, but also for those who choose them as a secondary destination or place to visit during their stay. This last option may involve the proliferation of negative effects, especially if it is done in a disorderly manner, while the economic benefits may be of minor importance.
The literature recognizes that natural protected areas are centers that attract visitors. However, studies analyzing tourist activities carried out in them approach varied themes, which do not normally include their capacity for attracting visitors from the vicinity. A clear deficiency is therefore revealed [20] which must be analyzed if we really want to develop management models which are adapted to the needs and peculiarities of each territory. Ascertaining the origins of visitors from the vicinity may serve as a basis for setting in motion a governance model which seeks to organize their visits, thus encouraging the tourist experience but also minimizing the impact generated in some areas as a consequence of the massive influx of visitors who are not controlled in any way. As a result, the case study takes as a reference the main protected natural spaces of Extremadura, Spain, to determine whether significant flows of visitors occur from the main tourist cities of the area, Cáceres and Mérida, which have been declared World Heritage sites.
In keeping with the foregoing, the main objective of this paper is to confirm the existence of flows of visitors to the natural spaces of Extremadura from emblematic accommodation areas of the autonomous region as a whole. Achieving this aim involves secondary objectives, among which are determining the capacity of attraction of the areas depending on the time of year and the importance of travel time in deciding on one place or another, and corroborating that tourists visiting Extremadura have mixed profiles combining cultural and natural elements.

Case Study
The area chosen to carry out the study is Extremadura (Figure 1), an inland region characterized by its rich and varied cultural and natural heritage. For this reason, it has an outstanding capacity for attracting tourists who seek, in particular, the enjoyment of the aforementioned resources. It stands out as a dual destination in that there is considerable complementarity between cultural and natural tourism, which makes it a privileged space in which to analyse the movements of tourists and at the same time confirm the complementarity of resources to attract visitors not only to the place of accommodation but also to the surrounding area.
The mobility of travelers once they reach their destination has attracted the attention of numerous authors, as there is interest in differentiating the expansion of activity to different places from that of accommodation. In the present case, we selected a sample of tourists who spent at least one night of accommodation in Cáceres or Mérida. These two cities constitute the main centers of tourist attraction: in 2017, over 500,000 tourists visited them if we consider only hotel accommodations; if all types of accommodation are taken into account, almost 800,000 overnight stays were recorded that year. Furthermore, we attempted to analyse the attraction to protected natural areas by this type of visitor. The mobility of travelers once they reach their destination has attracted the attention of numerous authors, as there is interest in differentiating the expansion of activity to different places from that of accommodation. In the present case, we selected a sample of tourists who spent at least one night of accommodation in Cáceres or Mérida. These two cities constitute the main centers of tourist attraction: in 2017, over 500,000 tourists visited them if we consider only hotel accommodations; if all types of accommodation are taken into account, almost 800,000 overnight stays were recorded that year. Furthermore, we attempted to analyse the attraction to protected natural areas by this type of visitor.
Despite the interest in analysing the capacity of attraction of protected areas based on their extensive territorial development, we chose to look at some of the most emblematic places in order to measure their capacity of attraction. For this reason, we took as our references a natural park, two nature reserves, and a geopark. These areas are outstanding treasures with varied ecosystems and, in some cases, prime examples of Mediterranean woodland in which water is also a key component. To be precise, the areas are Monfragüe National Park, the Villuercas-Ibores-Jara Geopark, the Tajo Internacional Nature Reserve, and the Garganta de los Infiernos Nature Reserve. Each is characterized by various levels of protection, and moreover they have varied characteristics based on their location, which gives them different degrees of accessibility.
These places are of great interest to visitors to Extremadura, as has been revealed in certain studies published by the Extremadura Tourist Observatory [41]. Among them, Monfragüe National Despite the interest in analysing the capacity of attraction of protected areas based on their extensive territorial development, we chose to look at some of the most emblematic places in order to measure their capacity of attraction. For this reason, we took as our references a natural park, two nature reserves, and a geopark. These areas are outstanding treasures with varied ecosystems and, in some cases, prime examples of Mediterranean woodland in which water is also a key component. To be precise, the areas are Monfragüe National Park, the Villuercas-Ibores-Jara Geopark, the Tajo Internacional Nature Reserve, and the Garganta de los Infiernos Nature Reserve. Each is characterized by various levels of protection, and moreover they have varied characteristics based on their location, which gives them different degrees of accessibility.
These places are of great interest to visitors to Extremadura, as has been revealed in certain studies published by the Extremadura Tourist Observatory [41]. Among them, Monfragüe National Park stands out as the most visited natural space; in 2017, 24.8% of travelers mentioned that they had visited it or intended to do so during their stay. This internationally renowned place is complemented by other well-known areas such as the Garganta de los Infiernos Nature Reserve, which is very popular in the summer months due to its morphology; its riverbed runs through a granite substratum in which potholes are present. This shapes an extremely attractive landscape which is visited by 15.9% of travelers to Extremadura. The list of protected areas is completed by the Villuercas-Ibores-Jara Geopark and Tajo Internacional Nature Reserve, which have become emblematic places for unusual market niches such as geotourism, or religious tourism in the former and river cruise tourism in the latter. These areas attract 8.6% and 7% of travelers visiting Extremadura, respectively.
The figures given show that natural areas are very attractive to those who choose the region to enjoy its natural or cultural resources. For this reason, the study takes a closer look at the capacity to attract visitors from more distant points to the two most visited cities of Extremadura, Cáceres, and Mérida. The demand of these two tourist centers is apparently strongly focused on cultural tourism, so in principle it could be assumed that natural places would not attract the interest of this sector. However, research reflects quite the opposite, i.e., that there is a significant demand for getting to know and enjoying the main attractions of a place [36,37].

Methodology
The information used to carry out the study came from three very different sources: the Register of Tourist Companies of the Regional Government of Extremadura, the Extremadura Tourist Observatory, and the National Geographical Institute. Each source provided information on available accommodations, tourist demand, and the national topographic database at a scale of 1:100,000.
All data are from the 2017 calendar year, although the accommodations considered were those available on 31 December of that year. Meanwhile the information on demand was obtained from 2854 surveys carried out between 1 January and 31 December 2017 in the tourist offices of Extremadura. The cartography selected was that available for 2017, although as can be seen from consulting its metadata, part of the information did not change since 2015.
Given the nature of the research, the key information for carrying it out was that provided by the survey, the technical specifications of which are shown in Table 1. These are reasonably reliable, as in the most unfavorable cases the margin of error is 2.3% for Cáceres and 2.6% for Mérida, taking into account a level of confidence of 95%. The survey recorded miscellaneous information about the visitors' profiles, preferences, and opinions, the natural areas they visited, the date, and the type of tourism they engaged in (Table 2).  As far as geographical data are concerned, thematic information at a scale of 1:100,000 was available, which was sufficient resolution for the purpose of the research, and was suitable for 20 meters. It served as a medium for the generation of a GIS project based on ArcGIS v. 10.5 software, on which was implemented the alphanumeric data of supply and demand, facilitating the shaping of a topological network defining the road connectivity that characterizes the region.
The network analysis was designed using the cities of Cáceres and Mérida as starting points, while the destinations selected were Villarreal de San Carlos (in the center of Monfragüe National Park), Cedillo (where there is a jetty for river cruises within the Tajo Internacional Nature Reserve), Cabezuela del Valle (the nearest settlement to the Garganta de los Infiernos Nature Reserve), and Guadalupe (the most visited settlement of the Geopark).
In order to calculate impedance, the maximum limits established for each channel were used, although given the deficiencies of the cartography it was impossible to include the lower limits found on certain sections. For this reason, it was constructed maintaining generic speed limits: on dual carriageways the maximum speed is 120 km/h, on two-way main roads it is 90 km/h, on B-roads it is 80 km/h, and in built-up areas it is 50 km/h.
As it was not possible to obtain more precise values, the duration of travel was complemented by means of Google Maps. The highest accuracy was achieved by the travel planner, which allowed calculation of the fastest routes by network analysis, and the travel time allocated was that obtained from the Google tool. In this manner, an approximate cartography was achieved of the usual journeys which occur between the towns with overnight stays and the natural spaces analyzed, determining the isochrones from the starting point to the destination. The data of the statistical analyses established from the replies given by the tourists were implemented in this cartography.
The starting point for the methodology proposed ( Figure 2) took the form of three clearly differentiated stages: compiling information by means of surveys, implementing this information in a geographic information system, and processing it by means of network analysis.
people, increasing the pressure already exerted by visitors from other places who have not been analysed and naturally by tourists staying there or in their areas of influence. This manner of proceeding gives us an idea of the success of natural spaces as tourist attractions for those visiting the two most prestigious destinations of Extremadura, although the possible impact of the influx of visitors must also be stressed. Then, the surveys were processed and a simple statistical analysis was carried out. To be precise, we resorted to a distribution of frequencies, as this simple technique has been used on many occasions in order to provide basic information on demand. This allowed us to find out the percentage of tourists who traveled to the protected areas from the sites with overnight stays. In turn, that made it possible to learn other important aspects so as to understand the structure of demand, among them the motivations mentioned for visiting Extremadura, in order to obtain an approximate profile of the tourists.
Finally, the statistical results were included in a geographic information system, which allowed us to obtain the routes tourists probably used and were calculated by means of a network analysis and verified by Google Maps. All this allowed an understanding of mobility according to the main parameters affecting the motivation of demand. This analysis of the movement of tourists once they reach their destination allowed us to find out the capacity of attraction of protected areas with regard to demand. It was carried out considering the variable timeframe of the attractions by means of a seasonal study. It was also analyzed considering the type of tourism engaged in by visitors.

Profile of Demand
The structures of demand for visiting the cities of accommodation as well as the protected natural spaces analyzed show characteristics common to the remainder of demand, although there are also considerable differences in some aspects (Table 3). The methodology began with surveys of tourists staying in Cáceres and Mérida, which were subsequently filtered in order to take as a reference tourists visiting any of the protected natural areas examined in the study. The starting point was 2854 surveys, which, after eliminating tourists who traveled to any of the protected areas in a complementary manner, was reduced to 1638, which accounts for 57.4% of tourists staying there. If we extrapolate the results of this sample to the number of tourists who spend the night in both cities, the natural spaces could host a very large number of people, increasing the pressure already exerted by visitors from other places who have not been analysed and naturally by tourists staying there or in their areas of influence. This manner of proceeding gives us an idea of the success of natural spaces as tourist attractions for those visiting the two most prestigious destinations of Extremadura, although the possible impact of the influx of visitors must also be stressed.
Then, the surveys were processed and a simple statistical analysis was carried out. To be precise, we resorted to a distribution of frequencies, as this simple technique has been used on many occasions in order to provide basic information on demand. This allowed us to find out the percentage of tourists who traveled to the protected areas from the sites with overnight stays. In turn, that made it possible to learn other important aspects so as to understand the structure of demand, among them the motivations mentioned for visiting Extremadura, in order to obtain an approximate profile of the tourists.
Finally, the statistical results were included in a geographic information system, which allowed us to obtain the routes tourists probably used and were calculated by means of a network analysis and verified by Google Maps. All this allowed an understanding of mobility according to the main parameters affecting the motivation of demand. This analysis of the movement of tourists once they reach their destination allowed us to find out the capacity of attraction of protected areas with regard to demand. It was carried out considering the variable timeframe of the attractions by means of a seasonal study. It was also analyzed considering the type of tourism engaged in by visitors.

Profile of Demand
The structures of demand for visiting the cities of accommodation as well as the protected natural spaces analyzed show characteristics common to the remainder of demand, although there are also considerable differences in some aspects (Table 3). As is logical, there is equal distribution between male and female tourists in both cities and in the region as a whole. This situation varies from that of the habitual places of residence of visitors who spend the night in Cáceres or Mérida; 80% are Spanish and 20% are from other countries. On average in Extremadura, however, foreign tourists represent less than 10% of the whole. The strong power of attraction of World Heritage cities compared with other destinations can therefore be appreciated. The type of demand is thus different, and this may condition the desire to get to know not only the cultural heritage of the accommodation cities but also the natural heritage of the surrounding area. As many as 65.4% and 68.2% of foreign tourists staying in Cáceres and Mérida who took part in the survey visited a natural space considered in the analysis. In contrast, only 34.6% and 31.8% declared that they would not do so, and only a tiny percentage did not answer the question. The same situation was found for demand by Spaniards, although the percentages are lower; only 58.6% of those spending Land 2020, 9, 47 9 of 22 the night in Cáceres and 55.5% of those staying in Mérida said they traveled to the areas under analysis, compared with 41.4% and 44.5% who did not.
The above proves a double demand clearly defined in two basic preferences. On the one hand, we can emphasize tourists who are only attracted by the cultural assets of the towns providing accommodation; on the other hand, an even higher percentage of tourists not only seek cultural resources but also wish to get to know the best known protected areas of Extremadura. This behavior strongly suggests the existence of a clear market niche with a mixed demand by tourists who assess resources according to their quality.
Likewise, these areas attract visitors between 36 and 65 years of age; proportionally the number of those 46 to 55 years of age is slightly higher. This pattern does not vary significantly among the areas analyzed and Extremadura as a whole and thus may be a good indication of the predominant ages of tourists. Furthermore, they generally travel as a family or with a partner; those who do so as part of a group or alone are of little relative importance, accounting for less than 10% of the total.
Differences can be appreciated in the analysis of overnight stays, as in the cities analyzed nearly 30% of those polled spent more than five nights at their destination compared with the average for the region, 23.9%. These figures can be put into perspective if we consider that over 63% stayed four or more days in Cáceres; for Mérida, that falls to 53% and for Extremadura as a whole to 45%. The fact that average stays are longer in World Heritage cities is corroborated by the finding that the percentage of tourists staying only one or two nights is substantially lower.
They tend to choose hotels or similar accommodations, and indeed the subsector of hotels accounts for a large percentage of stays with figures much higher those of the region as a whole.
This brief characterization of demand allows us to obtain a profile of the typical visitor as a person who travels with a partner or with his/her family, is between 36 and 55 years of age, and spends five or more nights at a hotel. In other words, we are concerned with a long-stay tourist, in contrast to the average stay in hotel-type accommodations, which, according to the National Institute of Statistics [42] for the year analyzed, is fewer than 1.8 days.
This fact, and the fact that they stay in historic cities and not in the natural spaces they visit, may be a clear indication of possible problems which have already been contextualized in the literature, such as the use of natural spaces for excursions, which may have an impact on the environment and provide questionable benefits, as it does not involve staying the night. Together with the availability of accommodations in the protected spaces or in the vicinity, this may cause a conflict of interest if they do not spend the night in these spaces.

Mobility and Seasonality
With regard to the two cities analyzed, it is emphasised that some tourists make use of their stay or their return to their places of origin in order to visit emblematic places of acknowledged prestige. Despite this, and although both Cáceres and Mérida have good road networks, there is a clear difference between the number of tourists staying in each city who decide to travel to the protected areas analyzed. In this sense, it should be stressed that 60.9% of those polled who stayed in Cáceres chose to visit at least one of those places. In contrast, only 45.5% of those staying in Mérida did so. This is a considerable difference that may be due to the distance from the overnight stay location to the protected areas, especially if we take into account that demand shows no significant difference between the two cities.
If Figure 3 is analyzed in detail, it can be seen that there is always a clear distinction between travel time and the percentage of visitors. The large number of visitors who choose Monfragüe compared with the other protected spaces stands out. The reason for this must be sought in its status as a national park and all this entails, from resources designed to promote it to aspects linked to the continuous improvement of the area it occupies. Moreover, it is in the vicinity of the two main dual carriageways that cross the region. Despite this, it can be observed that those staying in Cáceres tend to visit it more than those staying in Mérida, which makes it clear that travel time is an aspect to be taken into account. This same circumstance can be appreciated in the other protected spaces, although their level of attraction is noticeably lower owing to distance and the fact that they enjoy a lower level of protection, which means the demand may be assumed to be lower. their level of attraction is noticeably lower owing to distance and the fact that they enjoy a lower level of protection, which means the demand may be assumed to be lower. As a general rule, a decrease can be observed in the percentage of visits as distance increases; the threshold is 80 minutes for the outward journey. Moreover, it can be appreciated that more distant areas are visited by fewer tourists. This reflects that both the location of the area and travel time represent challenges for tourist mobility and consequently in achieving orderly tourist development in those areas, which are also characterized by having limited accommodations. The general picture described above is of necessity complemented by another more detailed one, in which the capacity of attraction of natural spaces fluctuates considerably according to the time of year when the analysis is carried out, as shown in Table 4. It is therefore revealed that there are noticeable distances between the mobility of tourists staying in Cáceres and Mérida, as the former is nearer to the protected spaces. Likewise, it is evident that Monfragüe National Park is the place most often visited by those staying in Cáceres, followed by the Garganta de los Infiernos and Tajo Internacional Nature Reserves and the Geopark, thus maintaining the order established depending on distance. In contrast, it is slightly different for tourists staying in Mérida, although Monfragüe continues to be the most popular place to visit, followed by the Geopark and the two nature reserves.
The preferred season for enjoying this type of area is spring, followed at some distance by summer and, to a lesser extent, autumn. The least travel is recorded in winter. As a general rule, a decrease can be observed in the percentage of visits as distance increases; the threshold is 80 minutes for the outward journey. Moreover, it can be appreciated that more distant areas are visited by fewer tourists. This reflects that both the location of the area and travel time represent challenges for tourist mobility and consequently in achieving orderly tourist development in those areas, which are also characterized by having limited accommodations.
The general picture described above is of necessity complemented by another more detailed one, in which the capacity of attraction of natural spaces fluctuates considerably according to the time of year when the analysis is carried out, as shown in Table 4. It is therefore revealed that there are noticeable distances between the mobility of tourists staying in Cáceres and Mérida, as the former is nearer to the protected spaces. Likewise, it is evident that Monfragüe National Park is the place most often visited by those staying in Cáceres, followed by the Garganta de los Infiernos and Tajo Internacional Nature Reserves and the Geopark, thus maintaining the order established depending on distance. In contrast, it is slightly different for tourists staying in Mérida, although Monfragüe continues to be the most popular place to visit, followed by the Geopark and the two nature reserves.
The preferred season for enjoying this type of area is spring, followed at some distance by summer and, to a lesser extent, autumn. The least travel is recorded in winter.
The overlaps of main motivations driving demand and prompting travel to these areas are also of note. Among them, the practice of cultural visits stands out; it is not for nothing that the cities chosen for accommodation are characterized by their clearly cultural attributes, to which gastronomy can also be added as a very important and strongly linked feature. In addition, the practice of rural tourism in its widest sense-ranging from the enjoyment of rivers and canyons to birdwatching-is of considerable significance, which confirms the existence of a mixed cultural and rural demand and partly justifies travel from some areas to others. This situation characterizes both cities, although it affects the natural spaces analyzed on different levels. In this case, it can be highlighted that although gastronomy is important on several levels, there are specific reasons affecting some of these levels. Such is the case of motivation linked to the aquatic features, and Garganta de los Infiernos can be singled out as it is one of the most attractive bathing areas in Extremadura and highly representative. To be precise, it accounts for over 17% of the responses of those polled, while the others areas barely exceed 11% for those who stayed in Cáceres and do not even reach 10% among those who stayed in Mérida. On the contrary, birdwatching predominates in Monfragüe, which is a well-known ornithological destination, and also in the Tajo Internacional Nature Reserve, an area of unspoilt nature which also has numerous bird species. On the other hand, visits to geological formations are more frequent in the Geopark than in other areas.
When analyzing journeys to the protected spaces made by those staying in Cáceres (Figure 4), the effect of proximity or, more precisely, travel time becomes clear. Figure 4 emphasizes that Monfragüe, 66 minutes away from the city, is the most visited protected area, although its capacity of attraction varies greatly depending on the time of year. In spring, it receives 11.9% of tourists who spend the night in Cáceres. This percentage falls in summer and autumn to around 8%. Winter is evidently when there are the fewest visitors.
The second most visited natural space is the Garganta de los Infiernos Nature Reserve, which is very popular, especially in spring (5.2%) and summer (4.8%). In contrast, its attraction is considerably lower in autumn (2.3%) and almost non-existent in winter (0.3%). This variability is caused by its difficult access, as visitors can only access the area on foot, although it can be reached from the nearest settlement in barely 90 minutes and is a destination linked to bathing.
On the other hand, the Villuercas Geopark and the Tajo Internacional Nature Reserve show similar percentages, as spring and summer are the seasons in demand, with values fluctuating between 4% and 2.1%; autumn and winter are of little importance. It should be stressed that both areas are almost 2 h away from Cáceres, which means that their capacity to attract visitors is lower. Apart from the distance, it should also be mentioned that travel is mainly on two-way and regional roads, which are narrower.
The inference that can made from analyzing journeys made by travelers from Mérida ( Figure 5) is that Monfragüe National Park is the most popular place for tourists whatever the season, although spring has the largest influx of visitors (8.4%), followed by summer and autumn, with much lower values of 5.7% and 4.7%, respectively; in contrast, winter accounts for barely 2% of visitors. These are logical figures if we consider that the travel time from Mérida to Villarreal de San Carlos is almost 2 h.
On the other hand, the Villuercas Geopark and the Tajo Internacional Nature Reserve show similar percentages, as spring and summer are the seasons in demand, with values fluctuating between 4% and 2.1%; autumn and winter are of little importance. It should be stressed that both areas are almost 2 hours away from Cáceres, which means that their capacity to attract visitors is lower. Apart from the distance, it should also be mentioned that travel is mainly on two-way and regional roads, which are narrower. visitors are attracted to the area, and winter continues to be the least popular season. Garganta de los Infiernos attracts 7.4% of tourists who stay in Mérida despite the fact that it is more than 2 hours away from the city; the percentages for spring (3%) and summer (2.5%) are very similar.
Finally, the Tajo Internacional Nature Reserve, which is also over 2 hours away, captures less than 6% of tourists who spend the night in Mérida; they mostly visit the reserve in spring and summer. The motivation that drives demand by visitors staying in World Heritage cities who visit the protected places varies, as shown in Table 5. Despite this, it is relatively homogeneous compared to the group of tourists who do not visit any of the natural areas of Extremadura.  The second most visited place is the Geopark, which was chosen by 11.3% of those who spent the night in Mérida, from where the travel time is 106 minutes. Despite its strong capacity of attraction, it is much more popular in spring than in other seasons, accounting for 7.7% of visits. This might be related to the proximity of Guadalupe, which is a center of attraction for religious tourism, especially taking into account that spring and Easter coincide. The rest of the year, many fewer visitors are attracted to the area, and winter continues to be the least popular season.
Garganta de los Infiernos attracts 7.4% of tourists who stay in Mérida despite the fact that it is more than 2 hours away from the city; the percentages for spring (3%) and summer (2.5%) are very similar.
Finally, the Tajo Internacional Nature Reserve, which is also over 2 hours away, captures less than 6% of tourists who spend the night in Mérida; they mostly visit the reserve in spring and summer.
The motivation that drives demand by visitors staying in World Heritage cities who visit the protected places varies, as shown in Table 5. Despite this, it is relatively homogeneous compared to the group of tourists who do not visit any of the natural areas of Extremadura. The main motivation is cultural visits, which is self-evident considering that the accommodation centers are prime examples of cultural tourism in the region. This motivation is markedly different among those who intend to visit protected areas and those who do not; the average difference exceeds 13%. Furthermore, this contrasts with the similarity of replies of those traveling to the natural places.
The proportion of those polled who mentioned gastronomy as a motivation is also noteworthy; the percentage is higher for those who do not visit natural areas (21.2%) than for those who do (16% on average). However, when we consider the importance of the motives governing rural tourism, the similarity between both types of demand is greater.
The importance of those who take advantage of their stay to go birdwatching is also of interest; this is a key aspect of visits to Monfragüe and the Tajo Internacional Nature Reserve. In contrast, the motivation governing visits to rivers, reservoirs, and canyons has a strong link with the Garganta de los Infiernos Nature Reserve. On the other hand, visits to mines, caves, and geological formations are concentrated in the Geopark.
This brief summary shows that demand is a response to specific orientations and governs tourist travel owing to the inherent characteristics of the natural spaces. Indeed, it is clearly shown that there are specific segments of the tourist population who seek specific elements such as birds, geological formations, or bathing areas. The territorial analysis corroborates that each natural place has its own peculiarities that make it especially attractive, as can be seen in Figure 6. It is clear that if we consider the capacity of attraction of each area in accordance with three specific tourism niches, a framework can be erected on which to base both product design and sectoral planning. These opportunities would concentrate on the current success of ornithological tourism, bathing tourism, river tourism, and geotourism.
The seasonal analysis of motivation reveals a very similar situation, as can be seen in Table 6. It shows that tourist mobility drops sharply in winter, when minimum figures are recorded, as the season is less favorable for enjoying the protected areas owing to climatic factors, daylight hours, etc. During this period tourists are more motivated to engage in cultural tourism. This is characteristic of tourists who stay in Cáceres, although for those who stay in Mérida the seasonal differences between those who do and do not visit the natural areas is less clear.
the percentage is higher for those who do not visit natural areas (21.2%) than for those who do (16% on average). However, when we consider the importance of the motives governing rural tourism, the similarity between both types of demand is greater.
The importance of those who take advantage of their stay to go birdwatching is also of interest; this is a key aspect of visits to Monfragüe and the Tajo Internacional Nature Reserve. In contrast, the motivation governing visits to rivers, reservoirs, and canyons has a strong link with the Garganta de los Infiernos Nature Reserve. On the other hand, visits to mines, caves, and geological formations are concentrated in the Geopark.
This brief summary shows that demand is a response to specific orientations and governs tourist travel owing to the inherent characteristics of the natural spaces. Indeed, it is clearly shown that there are specific segments of the tourist population who seek specific elements such as birds, geological formations, or bathing areas.
The territorial analysis corroborates that each natural place has its own peculiarities that make it especially attractive, as can be seen in Figure 6. It is clear that if we consider the capacity of attraction of each area in accordance with three specific tourism niches, a framework can be erected on which to base both product design and sectoral planning. These opportunities would concentrate on the current success of ornithological tourism, bathing tourism, river tourism, and geotourism.

CÁCERES MÉRIDA
(a) (d)   Nevertheless, when the motivation for visiting the various places is studied in detail, interesting differences can be found between them; this confirms the demand by those staying in the two World Heritage cities. It can be observed that the Monfragüe National Park is visited in all seasons by tourists who not only enjoy cultural and gastronomic visits, but are also attracted by rural tourism and birdwatching, which is very popular from spring to autumn. In contrast, other places linked to bathing or river-based leisure attract many visitors in spring and summer, as is the case for Garganta de los Infiernos.
An overall analysis of visitors spending the night in both Cáceres and Mérida shows that their preferred activities are cultural visits, gastronomy, and rural tourism. However, birdwatching and aquatic tourism are considerably less popular as they are more seasonal, the former owing to the ethology of birds and the latter owing to the weather required for bathing. Furthermore, visiting geological formations is of little importance, with the exception of the Geopark.

Discussion
In recent decades, it has been observed that protected natural spaces have evolved from being merely strongholds of fauna and flora characterized by outstanding ecosystems to becoming tourist areas in great demand. They combine a conservation function with another linked to enjoyment and recreation, giving rise in many cases to the intensive use of particularly sensitive areas. By means of this exploitation, the aim is for these spaces to achieve socio-economic development in line with other areas [43,44]. However, this use as tourist destinations may generate considerable environmental impact, which necessitates establishing tourist policies with governance models designed to minimize the impact.
Despite this need, significant gaps in the literature can be found. Although exhaustive knowledge has been obtained on the environmental aspects of these areas, the same cannot be said for the way they are exploited by tourism, as in many cases estimates are made of visitors to some areas but other aspects are ignored. In analyses of protected spaces, this deficiency is of particular relevance when other aspects such as the capacity to attract tourists staying in nearby areas is unknown. For this reason, it is understandable that the mobility of visitors must also be analyzed, placing special importance on the accessibility of these areas as they affect visitor satisfaction and behavior [45].
Analyzing the mobility of tourists once they reach their accommodation location is most important, in that it allows tourist policies intended to create specific products to be designed. These must be understood from a sustainability perspective, which is not easy to achieve considering that most visitors travel freely on their own and only in certain cases engage in specific activities in which they are guided within these places and minimize impact.
The use of private cars is encouraged, as this allows mobility in many protected areas, which leads to highly visible impact if these areas are crossed by communication infrastructure.
We therefore question the sustainability models proposed by ecotourism, as their marketing and the risks of the chaotic development of the activity have been mentioned on numerous occasions in a highly critical manner [46,47]. As a consequence, studies aiming to plan ecotourism routes in nature reserves are beginning to appear in the literature [48].
With this background, the majority of existing studies concentrate on measuring mobility based on a destination. More than two decades ago, this gave rise to interesting studies combining tourism and urban mobility [49], timeframe heterogeneity [50], and the role played by tourists regarding mobility [51,52]. There is even a tendency to analyze mobility by means of Big Data. There are, however, very few references to the study of tourist flows towards natural areas. For this reason, in many cases the analysis of these areas is incomplete, as their actual attraction capacity remains unknown. It should be considered that although in some areas visitor surveys have been carried out, these concentrate on their place of origin and not on their accommodation location.
For all these reasons, it can be seen that emphasis is rarely placed on journeys made by tourists from their accommodation location to other places. In other words, the activity of taking trips has not been analyzed in detail, which, as has been revealed, may result in large flows of visitors, although the economic benefits are substantially lower as there are no overnight stays even if services and equipment are used [53]. This negative impact generated by the uncontrolled flow of visitors may become a serious problem, especially when trips are taken in protected natural environments and individually by the travelers themselves. It indicates not only a lack of planning, but also little environmental awareness, as the uncontrolled influx of visitors may lead to considerable impact on specific points of the territory, as occurs in the area under study.
Under these premises, the study carried out confirms the existence of flows of visitors who use resources but do not normally provide any kind of economic benefit for the territory. Indeed, in line with the main objective, we found that important flows exist which originate from areas outside the protected spaces. In the case chosen to illustrate this situation, we observed how the main focal points of tourist areas attract visitors to the protected areas analyzed. This corroborates the use of resources and the generation of tourist income in different places, from which it can be inferred that there is an impact and no profit is obtained.
The situation described becomes even more delicate considering that the flow of visitors varies depending on the time of year, as the attractions of the protected areas are also changeable. This may multiply the impact by concentrating a large number of visitors within a short period of time.
Likewise, we found that although some tourists are particularly interested in getting to know protected areas, visitors as a whole are highly heterogeneous, as shown in the case analyzed. This should be corroborated in other areas to find out whether different tourist profiles exist.
It is likewise confirmed that travel time is a key factor in measuring the attraction capacity of protected areas, considering at the same time that both protection categories and special features are important in persuading visitors to choose one place or another.
This contribution corroborates the attraction of natural areas for tourists staying elsewhere and who travel to them with very different motivations. An essential reason for this situation is the desire to visit cultural spaces, as is clear from the accommodation locations selected. Moreover, we were able to determine and specify the tourist flow generated and show that accessibility is a very important factor, taking travel time into account; furthermore, we provide a specific demand profile. With all this, the objectives established for the research have been met. It must, however, be recognized that this line of research still has certain limitations, which point to the need to request further information in future surveys on demand so that the influx of tourists attracted to such areas can be more closely defined.

Conclusions
The results of this research indicate that two types of conclusions, generic and specific, can be drawn regarding the areas analyzed.
Among the generic conclusions, we can mention the vital role natural areas have begun to play as tourist destinations; this goes far beyond the original concept of creating preserved areas. This tourist use has had a considerable impact, which has been well documented by the specific literature, although efficient governance is intended to minimise it. Nevertheless, certain studies confirm the existence of numerous gaps in the knowledge of the tourist phenomenon characteristic of these places, especially when aspects connected with mobility are considered. All this implies the need to continue with more detailed analyses of this unusual type of tourist destination, although owing to the idiosyncrasies of each protected area, specific cases must be studied with the aim of determining behavior guidelines.
Among the specific conclusions, it should be emphasised that the protected natural areas analyzed constitute important attractions in Extremadura. They are indeed visited by many people who stay in places at a distance from these areas. In this sense, we show that tourists staying in historical cities with strong links to cultural tourism represent a considerable volume of travelers to protected natural areas.
It is also clear that distance and, above all, travel time are key in assessing the capacity of attraction of any of these areas. The threshold is 60-80 minutes to reach them, although this is greatly exceeded when there is considerable richness of the surroundings and the tourists are sufficiently motivated, although the percentage of visitors is much lower. This confirms the importance of accessibility.
Likewise, we corroborate that Monfragüe National Park is the natural area in Extremadura which generates the highest demand, followed at some distance by the Garganta de los Infiernos Nature Reserve. The Villuercas-Ibores-Jara Geopark and the Tajo Internacional Nature Reserve are further down in the ranking.
We also observe how the capacity of attraction of a space varies considerably depending on the time of year. As a general rule, spring and summer are the most popular seasons with visitors, followed by autumn, and winter is the least favorable.
Finally, we found that it is possible to draw up a profile of a typical tourist visiting these areas from other points, which is that of a person 36 to 55 years of age, a resident of Spain with cultural and natural aspirations. Such tourists travel with their partners and generally stay in hotels for an average of 4 or more days. Funding: This publication is part of research carried out within the research projects "Diseño y elaboración de productos estratégicos diferenciados para la potenciación del turismo rural en Extremadura. De la detección de problemas a la propuesta de soluciones basadas en criterios geoestadísticos" (Code IB 16040) and "Análisis de