Ascent:
Mont Pourri, despite its name (rotten in French) is the second highest summit of Vanoise at 3779 meters. The peak is no more rotten  than elsewhere, and the very beautiful summit warrants a detour.

From Lac Marlou, take a small trail which runs along the south side of the lake. Climb in the direction of  Lac des Moutons without going there, then continue to follow the line of the Grand Col chair lift following the ski slope as best as you can, or the road, to arrive at the summit. From the summit of the chair lift, continue in the same direction until Grand Col which appears very close. It takes an hour from Lac Marlou. Grand Col has two refuges with about ten places where it is possible to spend the night with rough conveniences.

From Grand Col, follow a small trail in the moraine until the glacier of Grand Col around 3100 meters. Put on the crampons and tie on at this place. Climb on the glacier and via a circle arc under Aiguille du saint Esprit you reach the foot of Roches pass. Climb the glacier as best as possible, it may be very crevassed at the end of the season to reach Roches pass in an hour from the start of the glacier. From Col de Roches, locate a ledge downclimbing in rock equipped with spits and a cable. An easy downclimb follows, then continue descending by small ledges in the opposite direction to reach the Geay glacier at the foot of the rocks. Traverse slightly climbing to reach the normal Mont Pourri route leaving from Peisey Nancroix.

When you arrive in line with the summit, climb as best as possible on the snow slope which can come very close to 40 degrees. You reach the shoulder on the right of Mont Pourri which makes it possible take a breather before starting the final ridge. Finish by a ridge in snow then in rock to emerge on the summit. It takes 4 to 5 hours of climbing depending on the conditions of the glacier.

Descent:
The descent is done at the same place in the opposite direction. Be very careful on the slope at 40 degrees on Geay glacier as well as under Roches pass because the snow generally starts to transform despite the fact that it faces west.