The Blue Lagoon is a channel between the Maltese islet of Comino and the smaller Cominotto, and its colour does not come from the water. It comes from the floor. A bed of pale limestone lies a few metres down and throws the sunlight straight back up. The sea over it turns a blue no other bay in Malta has. The crossing to Cominotto is a short swim with that floor visible the whole way, so the light keeps arriving from below rather than above. Further out you reach the hard line where the pale sand stops and the bottom drops into navy. Back on the Comino side, low limestone shelves let you jump straight in, and the water is clear enough to see where you are going to land. Even in August the first second is a shock of cold.
A short walk up the bare hillside reaches Saint Mary's Tower, and from up there the lagoon reads as one bright seam between two dry islands, with Gozo across the channel and almost nothing built in the frame. The tower has done film work: it played the Château d'If, where Edmond Dantès is locked up, in the 2002 Count of Monte Cristo. Round the headland lies the Crystal Lagoon, a cove walled in by sheer cliffs where you swim straight off the boat because there is nowhere to stand, and its floor is rock rather than sand, so the water deepens from pale blue to bottle green. The same waves have cut caves and arches into the limestone, and small boats slip inside them. Comino also has residents who will not land in daylight: fifty to eighty pairs of yelkouan shearwater nest in these cliffs and wait offshore until dark, because gulls would take them at their burrows. Winter empties the channel altogether. The boats stop, the kiosks pack up, and the colour goes on lying over that white floor for the island's two permanent residents and the birds.