Cosmiques Arête

The Classic Climb. AD, Grade II, mostly snow and moderate alpine climbing, with a few sections of strenuous mixed climbing (in winter) or easy rock. A party competent at the grade will simul most of the route.

The start up from the Cosmiques laboratory is quite easy, no need to rope up. The beginning of the arete apparently is a slab in summer, but an easy snow slope in winter. Follow the path of least resistance (or tracks) more or less along the crest of the ridge. If in doubt turn features on the right. Eventually you will reach a high point with bolted rap anchors.

Use the rap anchors to belay yourselves or rap down to a col below (5-10m), traverse the saddle of the col to a gendarme, and rap from bolts on the gendarme. You can rap either skiers left or right, but skiers left is preferable in summer because rockfall in 2019 left a ton of choss on the face below the saddle and the rap on skiers right drops you down that way. The rap down skiers left keeps you away from the choss, but it's awkward. A 30m rap will take you all the way whichever way you go, but if going skiers left then it may be prudent to stop at an intermediate in-situ anchor to avoid corkscrewing your way all the way around the gendarme in one go since that could make it hard to pull your ropes. Try to be efficient. This is the biggest timesuck on the route, and frequently where you'll encounter traffic jams, but it's also a great exercise for people inexperienced with this kind of terrain, since longer and harder ridge routes can often involve a number of such maneuvers.

From the base of the raps follow a snowy ledge system along the right side of the arete to 5m 3c chimney with chiseled holds. At the top of the chimney there is a pin which is useful as a short belay point to avoid rope drag. The route continues down along ledge systems (still on the right side of the arete) and then back up to a shoulder (lots of up and down in rapid succession, hence the rope drag concern). From here the path of least resistance stays generally on the right side of the arete until you reach the Digital Crack (8a+) gendarme. This gendarme is classically passed on the left via an icy gully/hump that stays pretty close to the true ridge crest of the arete (cover of the Boscoe Chamonix guide, 1st ed, 2016), but sometimes the path goes right of the gendarme depending on snow coverage. The route flattens out a bit and opens up here for a short segment before the crux.

Take the crux (4a) right slanting finger crack on the south facing wall to a ledge with a bolt or two (5m), traverse the ledge right and follow a chimney up then step back left out of the chimney to a large flat pedestal. Bring your partner up, then traverse to the north side of the arete via the western end (climbers left) of the pedestal.

The climbing has changed substantially on the north side of the arete in the past few years (2022-2025). There is much less pro than I remember and instead a number of new bolts have appeared where previously there were none at all. Unless you've done the route before though, this is neither here nor there. It's hard to get lost at this point. Continue via the path of least resistance. You will climb a zig-zag system of ledges for about 5m at some point that is wildly exposed for how easy the climbing is, and then find yourself some distance above that confronted by a chimney. Sometimes this chimney offers some actual water ice (WI2) adding to the variety of climbing on the route, but I've also seen skiers (who would struggle to ski carry through the chimney) bypass it by turning it on the left and going up later. If you take the chimney though you top out on the right at the end and will find yourself at a pair of bolts with a summit plaque not far away. This is the end of the route.

Re: the chimney bypass, the original MP author of this route wrote "Traverse around the corner to the Chamonix side of the ridge, and don't get distracted by the gully with the small roof.. instead head further to the left for the last, brilliant pitch of mixed snow and ice climbing. Really a blast!". It's not clear to me (BP) if this description is still current given the changes to this route in recent years, but there is still a chimney bypass of some kind available as of March 2025.

Traverse the summit platform towards the midi station, climb the metal stairs and clamber over the railing at the corner of the observation deck. Notice the metal plate under your feet. Be considerate and take off your crampons before stepping off this and onto the wood.

5-8 cams, medium sized stoppers and whatever screws your carry for glacier travel. A single 60m rope is fine, and 50m would probably work.