FATMAP difficulty grade
This is a big mountain day traversing Castor, 4223m, the 17th highest major 4000m peak in the Alps.
From the Ayas Hut reverse your descent of yesterday, heading upwards, N, onto the broad shelf of the glacier then E, passing under Pollux.
You are now heading for the WNW flank of Castor, which you follow, becoming increasingly steep, to the top.
Aim for the L end of the summit ridge, just to the right of some rocks, as you reach the summit ridge.
Turn R and follow the knife edge ridge to the summit of Castor, 4223m.
This is memorable, never too hard but with an amazing sense of exposure.
The view from the top is stunning, with Pollux and the Breithorn now below you, and the huge bulks of Lyskamm and the Monte Rosa summits dominant in the immediate horizon.
From here there is an easy snowy ridge extending to the SE.
This crosses a subsidiary summit then over pt 4174m, before descending to the Felikjoch, 4061m, and skirting under the snowy top of the Felikhorn, 4087m.
Now head down the ridge towards the hut, aiming for the broad sloping glacial shelf which takes you under the Punta Perazzi, heading to the Quintino Sella hut at 3585m.