1. From Saas Fee take the cable car to Felskinn. From Felskinn take take the well marked path to the left. When you come to a skilift by the trail you can see the grey hut a kilometer away at the same elevation. Follow the well marked path to the hut. (20-40 minutes from Felskinn).
2. A bit longer approach is by taking the cable car from Saas Fee to Plattjen (2570 m). From Plattjen station take the marked path going to the direction of Saas Almagell (Don't follow the 'Saas Almagell' signs but the 'Britannia Hut' signs). The uphill will remain on your right.
The well worn path gains elevation slowly. The path from Saas Almagell joins this path near the Chessjen glacier. From here you can propably see the hut. Cross the little stream and the small Chessjen glacier.
From the Britannia hut take the path which descents to the Hohlaub glacier. Cross the glacier directly and aim to the saddle between Hohlaubgrat of the Allallinhorn and a rock hump. From the saddle the path descents a bit to reach the glacier again but stays close to the Allallinhorn wall.
Continue on the glacier to the direction of Adlerpass. The glacier is severely crevassed so be careful.
When you come to the end of the Allallinhorn East wall you are able to see the Allallinpass on the right. Continue that direction and gain some elevation. From here you can easily see the snowy part of the Rimpfischhorn north ridge which takes you to the beginning of the rock ridge.
After gaining some elevation on the Allallinpass cross the glacier to the base of the north slope. Ascent the snowy slope which gets a bit steeper in the end. The snow slope ends to the base of Grand Gendarme (4108 m.).
You can either climb to the top of the Gendarme or go around it on the East side (In my opinion it is best to get to the top and rappel from there). On the top there is anchor for rappeling (On the very top there are slings and cords but on the edge there are bolts). Rappel from the very top to the anchor 1/3 from the top of the Gendarme. From there you can reach the ridge with a 50 meter rope which you have doubled for rappelling.
The ridge consists of pretty loose rock in the beginning of the route. Stay near to the top of the ridge and continue further on. The ridge is very easily defined and you can hardly go wrong. Although, don't attempt this route in hard winds or on poor visibility. On some parts the rocks in the shadows may be really slippery because of the ice.
Follow a series of small gendarmes. The route gets a bit narrow every now and then but stay near the edge. Stay on the right side (Zermatt side) of the ridge top until you come to a large overhanging boulder which points to the left (to the direction of Strahlhorn). Take the left side of the ridge and continue on the wide ledge under the overhanging boulder.
After you have climbed several subsidiary summits the route gets noticeably steeper. This is the summit block which you climb by a narrow chimney on the left. On the top of the chimney you come to a slab which takes you right next to the top. There are pitons to mark that you are on the route. Climb the slab directly up and be careful of the loose rocks. Make sure your holds are solid so you won't drop rocks on your partner. On top of the slab there are lots of rocks suitable for belaying your partner climbing up. Continue the last few steps to the rocky summit.
The fastest way to get down from the top is to take the normal route to the glacier. From here travel the glacier to the Allallinpass and continue to the Britannia Hut.
Reversing is possible but takes almost the same time than the ascent. The gendarme is possible to climb on good holds when reversing the ridge (In my opinion it is best to take the glacier route to the Allallinpass).
A realistic time estimation for the route starting from the Britannia Hut would be around 7 hours. We did it in 5.45 but the going was pretty fast.
The route goes a long way on the glacier which is really hazardously crevassed. Be prepared for both self rescue and hauling your partner up from a crevasse. Every climber should carry at least two ice srews, 3-5 karabiners, prusiks and at least two slings. Crampons and at least one ice axe are a necessity.
On the rock ridge you might find it comfortable carrying a few nuts in case you want to place pros. We carried a set of nuts but did not place any. In most places you are able to find lots of suitable and solid rocks for belaying. You should be familiar with the technique.
Bring a full 50-60 meters length of rope. The Gendarme is 45 meters high so with a longer rope you could rappel it in ones but elsewhere on the route there is no use for a rope that long.
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