Hyskeir is a reef southwest of Canna composed entirely of pitchstone columns. On its northeast corner is one of the finest scenic dives around. A large cut in the rocks leads down to a cave at 8m that goes in 20 metres. Leaving the cave, head down a gorgeous gully to a sandy seabed. Keeping the colourful wall to your left leads to an amphitheatre with a white sand bottom past which huge shoals of fish swim. There’s always the chance of a passing basking shark. www.doune-knoydart.co.uk