The natural values and beauty of the Valsaín pine forests made the Boca del Asno meadow the favorite place for royal entourages to have a snack during their country walks while they spent the summer in the palace of La Granja. Starting in the 19th century, it became a meeting point for scientists, naturalists and hikers, who used to frequent the banks of the Eresma River in search of new paths of research, discovery and dissemination of knowledge through the study of the natural environment and outdoor activities. free. The recreational areas of El Robledo, los Encontros and Boca del Asno, all three located on the banks of the river Eresma, have become outstanding natural spaces for leisure and recreation that attract some two hundred thousand people a year. The picturesque name of Boca del Asno is due to the narrow narrowing of the riverbed, which crosses a narrow gorge with granite walls and the popular imagination compares it to the snout of a donkey, where small waterfalls, slides and pools are formed that they delight young and old alike in summer, when the temperature of the water is pleasant for bathing.
At the entrance of the car park there is a Sierra de Guadarrama National Park Visitor Center set up in an old forest house of the forest nursery. The center has route information and data of interest. The exhibition has an audiovisual of the Montes de Valsaín, the flora, the fauna and the territory of the summits. It also has thematic panels, projections and a room that develops the exploitation of pines and the use of wood as an economic resource. The visit is very interesting to learn about the natural, cultural and traditional world of the territory included in the protected area and the peripheral belt.