The wide corridor that descends (diagonally!) to Loch Avon from the top of Stag rocks, and is almost a mirror image of it's neighbour Y Gully. It is steepest at the top, but entry to the gully is often possible on skiers right. Once out of the gully, the snow filled debris runnel often offers a run almost down to the loch itself.
Approximate Start Height: 1040m
Approximate Descent: 290m
General Aspect: South
Climbing Grade: I
Notes: Fairly easy for Grade I
Excellent film of descent of Diagonal, Castlegates and 0.5, Feb 2013