To arrive to Benasque see main page of Posets. From Benasque take road A-139 to the Hospital of Benasque; after 4 km take a left by forest trail (0.5 km) to the parking of valley of Estós. From here to hut of Estós go to 2h15min (drop:+550m) follow the GR11 (paint red and white) near river Estós. This is a beautiful route across a little valley enclose by pine trees. The trail cross the "Torrente del pino" and take for right to the "Llano del Turmo" with a nice view of the mount Perdiguero. For the plains arrive easily to the mountain hut of Estós at 1895m. End of first day (you can walk around here). It's very hard only one day for this mount.
For the morning we're waiting 4h30min to the summit (drop: +1590m) Take the signaled GR-11 of col of Chistau (behind of the hut) to the river Estós. In the river follow to cross bridge and going up in direction to see a pass to glacier of La Paul (easy to here, 2h). In the glacier can be necessary crampons. Follow this desert of rock and snow to the "collado de La Paul" (3025m, 3h30min). Follow and you see the glacier of Posets and search for the right the break in the mountain with many attention (it's difficult to see). This pass can be difficult on some occasions (I+, 50º, with snow) and it can change every year but is the last obstacle to the ridge of Posets (some years is very hard to reach without snow). The snow in the glaciers is "alive", is advisable to request information in huts and refuges every summer for this route (the glaciers of all Pyrenees are in slow regression). Follow the ridge to the south and round the climb for the west to the summit.
Crampons and ice axe by the two glaciers. Climbing I+ grade, 50º sloping with snow at the end of route. Reserve is required to sleep in the hut of Estós.
This is the hard route. For normal route see the easier Eriste-Forcaus.