From Gabas to the Col du Somport

Depart from the town of Laruns, latitude 42.890507569485 (N 42° 53’ 26”), longitude -0.42834368170095 (W 0° 25’ 42”)

• Lake Castérau

• Leave on the right the path of the lakes of Ayous to follow on the left the wide horizontal path (sign GR108) which passes a bridge and then crosses the pastoral plateau of Bious. Upon entering the National Park, the markings become lighter. On the opposite side of the plateau the track climbs on a grassy ridge; leave the first trail on the left (towards the Col de Peyreget). 200 m further, crossing a stream, leave the track for the path in the grass on the left hand (arrow "cheese sale"). It describes a lace among hook pines and then climbs to the base of limestone cliffs. At the cattle park of the Cap de Pount hut (cheese sale), go down slightly to the right towards a plateau, then along the left side of the torrent by a path. Take a footbridge over the Gave de Bious (8.7 km / 2h45) and climb on the opposite bank by two large switchbacks in the grass. Find the pastoral track, follow on the left for 30 m then, from the first hut of the Hosse (1710 m - water point at the lower hut), continue on the marked path on the right. It gains altitude above the hut (beautiful view of the Pic du Midi d'Ossau), soon quite abruptly in rocky outcrops, under the authority of the cliffs of Pic Castérau. In the upper part, a final gap on the left brings you closer to a grassy promontory overlooking Lake Castérau (1943 m). The path runs along the lake on the left; On the west side of the lake, after a ruin and an enclosure, the trace brushes a cubic rock, then reaches a double intersection of Y-shaped trails (11 km / 4h00) with a large central block (1990 m).