From Oloron-Sainte-Marie, follow the signs for Spain (Jaca, Col du Somport), pass Fort du Pourtalet, and before the bridge over the Gave d’Aspe, turn right (in fact, go straight on, as the A-road turns left to cross the bridge), towards Aubis. Park at the authorised terminus, at a place called Terrailh (two car parks).
(S/E) With your back to the car park, continue along the track to the left, upstream to the water intake.
(1) Carry on in the same direction along the track.
(2) Turn right before entering the Pyrenees National Park and head uphill through the woods to the Col de Lagréou.
(3) Take another path to the right to descend towards the Aspe Valley, take the hairpin bend to the right along the path, then return to the car park (S/E).