WHS-collectors should do this beautiful hike first: from the eastern end of the Pradera de Ordesa, cross Río Arazas and climb steeply up through the woods on the valley's south side. This hardest part, called "Senda de los Cazadores" (Hunter's Path), in which you ascend 600m, takes an hour. Then it's level or downhill all the way along the high Faja de Pelay path to the 'Circo de Soaso', a rocky balcony whose centrepiece is the Cola de Caballo (Horsetail) waterfall. Return by the easy path along the bottom of the valley, passing through several waterfalls. This circuit takes 7 hours, so bring those picnic sandwiches and mineral water. (Summer 2010)