Full or half-day outings will give you time to do some exploring above ground, as well. A unique combination of current and tide patterns make Dellis Cay a prime beachcombing spot. Little Water Cay is a sanctuary for iguanas and Fort George Cay sports remains of an elaborate fortification built to defend Caicos cotton planters' exports. You can still see several iron cannons lying underwater. Ocean Outback will chauffeur you to the Provo's wild southwest shores to explore a pirate's cave with 200 year old stone carvings and experience outback snorkelling in little-visited waters.
Most charters provide equipment for use on their excursions - ask ahead of time to be sure.
Here's a guide to help you find the snorkelling sites around Grand Turk. Probably the best natural reef snorkelling spot on Grand Turk is off the southeastern tip of the island at White Sands Beach. Here a large area of coral extends from the shore out 100 yards where the edge of the coral creates a mini wall formation teaming with fish. The coral starts in about 2 feet of water and the maximum depth is 15 feet. At low tide you can actually see some coral peaking out of the water.