This little-known natural space has more three thousand-metre peaks than any other in the Pyrenees, among them Aneto and Posets, the two highest mountains. Its main entry points are in the Benasque Valley and the Chistau (Ghistaín) Valley, in Sobrarbe.

Outstanding places to see are the beautiful villages of the Chistau Valley, the area around the Viadós mountain refuge, the great number of peaks for mountaineers to try and the numerous tarns or glacial lakes to be found in this surprising place.