The Turneffe Islands are a large coral atoll about 40 km east of Belize City, enclosing a vast sheltered lagoon fringed by mangroves and reef. Together with Lighthouse Reef and Glover's Reef to the south, they form three of the Caribbean's four true atolls — a geological rarity in these waters.
Turneffe is primarily a diving destination. The walls and channels around the atoll offer some of the best dive sites in Belize: healthy hard and soft corals, abundant fish life, seasonal aggregations of hammerhead sharks, and excellent visibility. The entire atoll was designated a marine reserve in 2012. Accommodation is limited to a handful of dive lodges on the eastern rim; most visitors arrive on live-aboard boats or as day trips from Ambergris Caye or Belize City.
Lighthouse Reef, further east, is where the Great Blue Hole sits — a 300-metre wide, 125-metre deep sinkhole made famous by Jacques Cousteau. It's a long day trip by boat from the coast. The dive descends through stalactites into deep blue water, more dramatic in photographs than on the bottom; the real reward is the wall diving on the surrounding reef and the chance to see grey reef sharks massing on the outer edge.