Exuma is a chain of some 365 cays running southeast from Nassau in the Bahamas, and almost nothing here is deep. The cays sit on the Great Bahama Bank, a shelf of fine white sand under sunlit water only metres down, which throws the light back pale blue. The sand is largely ooid, microscopic grains of calcium carbonate laid down in layers by warm, tide-swept water. Where the bank drops into a channel, the same sea goes navy at once. Its most famous residents work those shallows. On Big Major Cay some twenty semi-wild pigs live along the shore and plunge in as the engines slow, paddling out to meet your boat with their snouts held high. Nobody can say how they got there. Sailors left them to fatten for a later meal, the stories run, or they swam ashore from a wreck.
On the sandbanks the tide uncovers you can wade a long way out with bright water on every side and the water still at your knees. There is no land in any direction and no line between sea and sky. Around the corner from the pigs, Thunderball Grotto is a cave in a small cay where light falling through an opening in the roof turns the inside into a blue aquarium, which you snorkel at low tide among schools of fish. The James Bond films shot here gave it the name. A day by boat runs between the cays, dropping anchor off empty beaches for a swim and lunch on the sand. On the sun-warmed rocks of the neighbouring cays heavy rock iguanas bask, a lizard that lives nowhere on Earth but the Bahamas. Much of that route lies inside the Exuma Cays Land and Sea Park, which in 1958 became the first reserve anywhere to protect land and sea as one thing: reefs, seagrass, cays and everything moving between them. Since 1986 nothing may be taken from its water at all, and queen conch, grouper and spiny lobster now breed there in numbers that spill out and restock reefs far beyond it.