The Tobago Cays are five uninhabited islets in the Grenadines, inside a four-kilometre arc of coral called Horseshoe Reef that takes the Atlantic swell and leaves flat turquoise water behind it. The reef does two jobs at once. It stops the ocean, and it also makes the floor that gives the lagoon its colour. The white sand is not ground-up rock but the reef itself, broken down and washed in. Off Baradal's south-western shore the seagrass grows in water shallow enough for you to stand in, and green turtles feed in it nose-down, coming up to breathe close enough for you to hear. They are the only sea turtle that eats plants as an adult, and they crop the same patches again and again, because grazed grass comes back shorter and better to eat.
You snorkel the inner edge of the reef, drifting on the current a few metres above the coral, since the outer face belongs to the ocean. Rays cross the sand channels and conch lie out in the open. Much of the hard coral is storm-broken, so it is the fish that carry the show now. Petit Tabac sits alone on the ocean side of the reef: white sand, a stand of palms and open Atlantic beyond. It played the island Jack Sparrow was marooned on in the first Pirates of the Caribbean. The burning palm grove in that scene was an effect; the trees are still there. Park rules keep the vendors to one strip of sand on Petit Bateau, where boat cooks grill lobster and snapper under a couple of tents. The anchorage is the strangest part. Boats slip through a gap and lie with no land at all to windward — just a white line of surf a few hundred metres off, and the swell dying before it reaches you.