Grace Bay's sand stays cool underfoot even at midday. It is barely mineral sand at all — ground-up coral, shell and soft white limestone, pale enough to throw back the heat it never absorbs. The beach runs a little over three miles along the north shore of Providenciales. It owes its stillness to a barrier reef about a mile out, which takes the ocean swell long before it can reach the sand. What is left inshore is a shelf of water so clear it reads as bands of colour: white where the bottom shows through, then green, then turquoise darkening to navy at the reef line. Wade in and the sea hardly deepens. Fifty metres out you are still standing, watching light ripple over the ribbed sand.
At the western end the coral heads of Bight Reef lie close enough to swim to from the beach, and green turtles graze the seagrass between them. The easterly trade winds push away the sargassum weed that fouls much of the Caribbean, so the sand stays clean. A few nights after each full moon, marine worms rise in the channels at the far end of the bay and spawn in pulses of green light. The reef offshore is one arm of the 340-mile system ringing these islands, reckoned the finest in the tropical Atlantic after the Mesoamerican. All of it sits inside the Princess Alexandra National Park: boats hold to 15 miles per hour, and nothing, not a shell and not a fragment of coral, may be carried away. Nobody built here until 1984, when the first hotel opened on an empty shore. Low resorts line the dunes today, but the sand itself stays public, and it empties the further you walk.