From Laruns, head towards Spain via the Col du Pourtalet. After the hamlet of Gabas, in a hairpin bend with a small car park on the left, turn right towards the Lac de Bious-Artigues (road closed in winter, which explains the sign "Interdit à Tous Véhicules" which can lead to confusion).
Two car parks are available. The first is on the edge of the lake and the other further down before you reach the lake.
Leave early, otherwise you'll have to park in the "lower" car park, which is an extra 30 minutes' walk.
(S/E) At the start of the walk, head towards Lacs d'Ayous. The path skirts the lake on the left, then leads into a forest.
After a concrete climb, reach the Pont de Bious junction.
(1) Leave the track and follow the GR®10to the right towards Lacs d'Ayous (signposted). It passes through a forest and twists and turns. It then leaves the forest and reaches a pastoral area. Continue on past a promontory behind which is the first lake, Lac de Roumassot.
(2) Walk alongside it. The path then continues along a waterfall to reach the second lake, Lac du Miey.
Behind a final promontory, with a gentler climb, you will find Lac Gentau with, above it, the Refuge d'Ayous from which you can enjoy a magnificent view of the lake with the Pic du Midi d'Ossau in the background.
(3) From the refuge, continue along the path that twists and turns along the feeder stream to Lac Gentau towards a ridge.
This leads to Lac Bersau, which you skirt to the left to reach, after a few metres, the pass between Pic de Bielle and Pic Castérau, the highest point of the route.
(4) Take the fairly steep path down to a fork at the bottom of the valley.
(5) Leave the Col des Moines path on your right and turn left onto the path leading down to Lac Castérau.
(6) Follow this path over a small rise and then wind its way down the scree to the path leading from the Hosse shepherd's hut.
(7) Go down to the left towards the bottom of the valley, following the valley. Leave the paths leading to the Pic du Midi d'Ossau on the right and descend to the Pont de Bious where you left the track to take the path.
(1) Then take the same path back down through the forest to Lac de Bious-Artigues.
(8) For the more courageous, turn left to walk around Lac de Bious-Artigues and back to the car park (S/E).