This dead ground reasons to borders of the Duratn river and corresponds to an area that goes from Villa de Seplveda to the dam of Burgomillodo, about 27 km extends in lands of the municipalities of Seplveda, Seblcor and Carrascal of the River. In this average section of this affluent of the Duero, the river has created a deep tube in a zone of limestone rock, the sickles, that in some points reach more than 100 meters of height. Natural park in 1989 was declared, in attention to its landscaping values, of flora and fauna. They honor its population of leonados vultures, one of the majors European colonies; besides other birds like egyptian vulture, real eagle, kestrels, real owl, hawk pilgrim are different three zones or ecosystems: the high woodland (in the zone superior), cut and the bottom of the valley To the natural value it is necessary to add the cultural patrimony of the zone. Besides Villa de Seplveda, who deserves separate mention, within the park we can find the hermitage Romance of San Frutos (that offers of better views of Sickles), the Cave of the Seven Altars (rock church visigoda) and the Monastery of Our Mrs. of Los Angeles of the Sickle. The park owns several recreational zones, panoramic views and routes of senderismo. In Seplveda the Center of Interpretation is placed, the House of the Park, where to obtain all the necessary data, and some permissions in circulating around areas of reserve of the park. One of the options more demanded by the tourism is the routes in canoe, by waters of the tube, being able to observe the flora and fauna from I milk fluvial.