Arête des Cosmiques is one of the most popular routes in the Mont Blanc massif. Photos from this route are ubiquitious in guide books and magazines featuring climbs in this area, and it is easy to see why. The route itself isn't too difficult, though it is not without some challanging sections, and throughout the trip climbers will enjoy outrageous views of the Vallée Blanche and the surrounding mountains. The climb is amazing and features a mix of short glacier travel from Aiguille du Midi station down to Vallée Blanche and then a beautiful ridge climb on mixed snow and rock. This should definitely be on a list of must-do climbs if you ever find yourself in Chamonix.
The climb begins and ends at Aiguille du Midi station. Start early to avoid the crowds and take the first telepherique for a ride that gains 9,000 feet to the station. Weave around tourists and head toward the ice tunnel that opens up to the exposed descent route to the glacier. Once you reach the glacier, traverse below the steep face of Aiguille du Midi toward Cosmique hut. The base of the climb starts just before the hut. This approach probably takes about 30 minutes.
Easy mixed terrain marks the start of the climb, and the climb starts getting more exposed after passing the first small summit. While it always seems like there is a rock tower blocking the way, you'll weave around or go up and over those, which makes the route a very interesting climb.
The crux is a short and exposed vertical wall, but because this route has seen so much traffic, some of the foot steps are worn deeply and are easy for your crampon to bite into. A couple of easier pitches will then lead you back to the station, where you have to climb a rickety ladder back as the tourists snap photos and look at you in awe.