From Saint-Aventin (Gourron road), go down to the mill. After 1.750 km on tarmac turn right after the trough, wide track becomes a path through the woods. Cross a paved road (km 4.4) then a narrow bridge to reach the village of Oô (km 6.8). Go over a bridge, then cross the main road and then take a paved trail and continue on a technical trail to Astau' plan (km 10.5). Go past the barns and head south to the bottom of Val d'Astau. Cross the Neste d'Oô and get to the right bank down to the Granges d'Astau (km 13). End of the course. Mountain bikes are not allowed on the GR trail to the Oô Lake. Possible return to Saint-Aventin taking the trail the other way round.