7. Belize Barrier Reef, Belize City Also known as “The Great Blue Hole,” the Belize Barrier Reef is one of largest barrier reefs in the world. It creates a natural ecosystem that includes atolls, several hundred sand cays, mangrove forests, coastal lagoons and estuaries. It's so vast that much of it remains undiscovered and only 10 per cent of the marine life on this reef has been identified. Every year, over 260,000 tourists scuba dive in the Belize Barrier Reef, and the crystal clear and warm, protected waters make it ideal for snorkelers and novice divers.