This was our second 4000-er of the day, after climbing Pollux in the morning. Route finding on Castor couldn't be easier, as there was a clear trail, and many others had climbed it even the same day. Very high on the flank, the zig zag trail went to the crest of the SW ridge shortly before the summit, not to the steeper N ridge. I suppose it depends on the conditions which way is easier. As it was, I estimate that the grade of the route was around F+.
For our descent, we followed the exhilarating knife edge ridge to the east, to the Felikjoch, where we turned south to Rifugio Quintino Sella. It was a fine day in the Alps!