The Western Valleys Natural Park is one of the recently created protected spaces of the Jacetania Area. Covering an area of 27,073 hectares it includes the municipalities of Aisa, Ansó, Aragüés del Puerto, Borau and the Hecho Valley. This is one of the best-preserved ecosystems of the surrounding area, due in large part to a considerably less aggressive building development than in other valleys. There are various different habitats within its limits – beech, black pine, pine and fir forests, meadows and high alpine pastures. As for fauna, the highlights are Brown Bear, Lammergeier, Griffon Vulture and White-backed woodpecker, while there are many protected insects and various endemic plant species.

The territory of the Western Valleys Natural Park is within the main Pyrenean range. The massifs of Bisaurín, Aspe, La Mesa de los Tres Reyes (The Table of the Three Kings) or Peña Forca are the most noteworthy mountains, all of which show signs of glacial erosion, characterized by U shaped valleys. Mountain tarns are also of particular interest, especially those of Estanés and Acherito. These mountains are principally of limestone, with some clay and slate, particularly in valleys such as Guarrinza. Karstic formations also abound.

The position of the Park, on the most westernmost edge of the Aragonese Pyrenees is a determining feature of the climate, which is clearly under Atlantic influence. This leads to fresh and abundant vegetation, with yew trees and extensive forests of beech, fir and black pine. The animal population is extraordinarily rich. In this land of the Lammergeier, Otter, Pyrenean Frog, Red Kite and Hen Harrier, there are still some remaining Brown Bears.