In order to make the description to the routes to climb the peaks of the massif and not only the Grand Vignemale I go to show the route to approach to Glacier of Ossoue in one page to use with the routes (in order to not repeat). It's the same normal route to all the peaks of Massif, except the Picos de Tapou and Petit Vignemale (but in this peak is very near the normal route from Bayssellance). In each peak I'll write the route to climb the summit from the glacier. It's important to know what the route from Barrage d’Ossoue cross the bifurcation to arrive to the Refuge de Bayssellance ( 20 minutes from this place). This point (2500m) is located near of Caves of Bellevue and it don't has any signal, but it you can find the path to both sides and the left goes to glacier and the right, with the paint of GR-10, it's the way to refuge.
Getting ThereAccess from the French side by road is from the East-West autoroute E80 (Bayonne to Toulouse) and the National road N21 via Lourdes and the D821 / D920 to Cauterets or the D921 to Gavarnie. There are airports at Pau and Toulouse.
Access from Spanish side by road from the N.W. or W. of the country: across Irun to cross to France, taking the road to Bayonne and the same French way.
Access from Spanish side in the centre of Pyrenees (near Huesca): the best option in the entry in French territory across Col du Portalet or Col du Somport. In winter many days this road is closed by the snow (or it requires the use of chains). D918 to Argelès-Gazost, D12 and D921 to Gavarnie.
If you climb from Bayssellance (2651m) initially you must descent to get the path what arrive from Barrage d’Ossoue, following the path with cairns and painting of GR-10 (red-white) to the point of 2500m. You've walked across this point if your trailhead was Barrage d'Ossoue but not if you reached the refuge from Pont d'Espagne.
From Barrage d'Ossoue:
You'll begin from the dam in the wide valley following the good path near the river (oulettes d'ossoue). In the end of the valley, near the waterfall, the path go to left side in direction to the rocks, but the path is always easy to follow with signals of paint of GR-10 (red and white). After a little descent (in Le Pont de neige) you'll walk in an exposed area before to descent to cross the river before the ascent across the long ramp to caves of Bellevue (2400m). You'll turn to left side in the area over the caves to find the important crossroad where's the bifurcation (2500m) to Refuge Bayssellance. The paint in GR-10 go to right to refuge but you'll turn to left side following the cairns in the rocky hillside with a very narrow path to the bottom of the glacier. The entry of the glacier is visible in left side under the pyramid peak Monferrat, and the length of glacier tongue is different each year and epoch. It's the point to use the crampons and ice-axe walking always in west direction leaving the crevasses in right side, before the turn to entry in the plateau glacier. From this point is accessible the normal route to Montferrat, Central, Cerbillona, Clot de la Hount, Grand Vignemale, Pitón Carré, Pointe Chausenque and Epaule Chausenque.
Crampons and ice-axe all the year (it's a glacier).
Rope?: in some days early in the season after a recent snowfall the crevasses are difficult to see (it's dangerous) and it's a good idea the use of the rope in the glacier.