The valley of Ordesa was the starting point (1918) of what is now the National Park of Ordesa and Monte Perdido, declared World Heritage Site by UNESCO. A superb valley, nestled between huge cliffs and faults and crossed by the river Arazas that shows up in the shape of waterfalls such as the one from the Strait or the famous Cola de Caballo (i.e., horse tail).
In the higher areas there are a number of peaks exceeding the 3,000 m height which form the French-Spanish border, namely the Taillon (3,144 m), El Casco (3,006 m), Marboré (3,248 m), Cilindro (3,328 m), Monte Perdido (3,355 m) or Soum de Ramond (3,245 m). Lower one can find la Gruta de Casteret, the interior of which features columns and fossil ice waterfalls. Further below, the slope reaches a succession of cirques and glacial valleys, such as Cotatuero, where the famous "Cotatuero pins" can be found, a via ferrata so to say.
Cola de Caballo
The journey to the Cola de Caballo (i.e., a waterfall named "horse tail") begins at the meadow of Ordesa and goes to the end of the valley following the course of the river Arazas. The road goes through the famous "beech forest", from which you can see the waterfall of the Strait. A little further up, when the valley gets wider, we find las gradas de Soaso, in other words, the river terraces of Soaso. At the end of the Valley, the Cola de Caballo waterfall.
Another way of reaching the Cola de Caballo is by ascending via the Faja de Pelay, and taking the senda de los cazadores (i.e., the hunters' trail) and then descending by taking the usual path of the Cola de Caballo. The first stretch of the road, until you reach la Faja, ascends a steep slope (720 m elevation gain) then the path meanders without going up or down. The views on the valley and on the walls of Gallinero or Fracuata are exceptional.
Trails in Ordesa brochure (pdf)