Park at the Pla de la Lau car park.
(S/E) Head to the Maison du Valier via the footpath just to the left of the track, heading south-east. Go around the house and continue along the shaded footpath on the left bank of the stream, following the signs to the Refuge des Estagnous. The footpath joins the track, which you should follow in the same direction, still on the left bank of the Ribérot.
(1) At the fork, turn left to cross the stream via two footbridges and climb up through the forest to reach an intersection at a clearing.
(2) Turn right and cross the Ribérot again to continue on its left bank until you reach the Nerech waterfall.
(3) Cross the stream on a metal footbridge and continue right on the winding path. Continue to the Caussis hut.
(4) Take the path on the left, still heading towards the Estagnous refuge.
(5) At the refuge, continue straight ahead on the path towards Mont Valier. The gentle slope gives way to a more difficult passage to the Col de Faustin, where a view of the Ariège peaks unfolds.
(6) Continue to the left, leaving the path to Mont du Petit Valier on your right. Reach the summit.
(7) Return along the same path to the Estagnous refuge.
(5) Turn right onto a path that is not always very visible but is well marked with yellow markings, until you reach Col de Pécouch.
(8) Descend northwards towards Les Lauzets, following the same path, which is still not very visible due to the rocks but is marked with yellow markings. Reach a scree slope which you will need to cross to get to Étang de Milouga.
(9) Cross the outlet and continue on an easier section to the small Taus hut. From there, climb a few dozen metres to the right and continue north-west to an intersection.
(10) Take the path that descends to the left, making numerous hairpin bends. Leave the path leading to the Aouen hut on your right and cross the stream to gradually enter an increasingly dense forest. At the end of the descent, cross the Ribérot and return to the Maison du Valier and then the car park (S/E).
. Personally, I only did it in two days, but it's certainly doable for a hiker who is experienced enough to do >2000m of elevation gain/loss and sets off very early, but it's a very demanding challenge for the vast majority of people.