6 - 8 hours.
One of the most popular routes in the valley. The scrambling is excellent throughout and the rock quality is consistently good until the initial part of the descent, but this is low-angled and brief. Other than the pegs on the first pitch and bolts on the abseil, the route is unequipped so you'll need a rack, albeit a fairly small one.
From the top of the Index chairlift, descend towards Lac Blanc for 50m then take the jeep track on the left which takes you up towards the Grande Floria and Aiguillette de la Floria. Just after the path branches off to the Grande Floria, the jeep track crests a small col and begins to descend rightwards. When it does this, cut off left and pass under the Aiguillette de la Floria and then climb up to the top of the Floria drag lift. 20m past the drag lift take a path off left, across the scree slope and under the foot of Pointe Gaspard before climbing the gully above, on the left initially, following a grassy path. Continue up the path to the col. The final rocky step to the col is up a left-slanting crack which may feel a bit tricky if wet, so you may be glad of a rope on this section. From the col, go east over 50m of easy ground, along a vague ledge system up and rightwards, underneath the Crochues west ridge to reach the foot of the chimney which marks the start of the route - around 1 hour from the chairlift.
4a. Climb the deep-cut chimney (4a, 35m) passing a couple of pegs on the way to a ledge with plenty of good spikes for belays. There are some loose rocks around the belay spikes, so be careful not to knock anything down.
Go up and rightwards (passing to the right of the big boulder on the skyline) and follow easy, grassy terrain to the crest of the Crochues west ridge. You should join the ridge near the bolt belay at the end of routes 2 and 3, although you can join it just about anywhere. Follow the ridge easily for 70m (you can walk below it on the left if it is busy or wet) until the ridge drops away steeply and you are faced with a short descent down to a tower.
3b. Descend towards the tower on the north side of the ridge for 5m, before coming around to the south side of the tower and making an easy but exposed traverse across the south face. A 10m abseil back onto the north side allows you to pass the next, smaller tower on its north side, before climbing a short wall and slab (3b) to regain the ridge crest. The slab section can be bypassed on the south side of the ridge by following a grassy path.
Continue easily along the crest with interest until the summit. From the summit descend 30m back down the ascent route before turning east and following the ridge easily to the (marginally higher) north summit.
From the north summit, descend to Lac Blanc by scrambling down the Crochues North Ridge for 100m to where the ridge widens out and becomes less solid. Drop off the ridge rightwards and descend a scree/snow slope eastwards towards Lac Blanc. This slope is often snowy well into the summer season but it is the ideal angle for glissading so you can normally get away without crampons. If you leave the crampons behind and realise you need them for the descent, it is possible to carry on along the Crochues north ridge towards the Col du Dards. Shortly before reaching this the ridge drops steeply away and from here, make a 20m abseil east to reach the scree/snow slope where the angle is much lower. Continue down to Lac Blanc and either return to the Index chairlift (45 minutes from Lac Blanc) on an undulating path or descend down to the Flégère cable car (90 minutes).
FA: P.le Bec & T.de Lépiney, 1920