My favourite swims are explorations, going around rocks and through channels, never sure what will be around the next corner, getting totally absorbed in the world of the sea. Great Mattiscombe, down near Start Point, is perfect for this. First I swam off towards the strange pointed pinnacles to the right of the beach, where I became obsessed by a green optical effect under some of the rocks. Then I swam along the coast, in and out of shimmering lagoons, where red anemones clustered like fat rubies in the white rocks, to a tiny hidden cove filled with white shingle. Then I found a beautiful cave which lured me in with its haunting light; I floated in the pool inside it looking up at the 'skylight' above and then down, through my goggles, at the swaying shingle below. Magical.