Belize

Three hundred kilometres of barrier reef — the largest in the northern hemisphere — running parallel to the coast a few kilometres offshore, with a shallow warm lagoon held between the two.

The cayes sitting on it are low sand islands with a single street, no cars, and a horizon in every direction. Underneath, the seagrass flats are busier than the islands: turtles grazing, rays crossing the sand, and a wall a little further out where the shelf drops into open blue.