The largest of the three atolls, Turneffe, is the closest to Belize City. It's one of the best spots for diving, thanks to several steep drop-offs. Only an hour from Lighthouse Reef and 45 minutes from the northern edge of Glover's Reef, Turneffe is a good base for exploring all the atolls.
The best-known attraction, and probably Belize's most exciting wall dive, is the Elbow, at Turneffe's southernmost tip. You may encounter eagle rays swimming nearby. As many as 50 might flutter together, forming a rippling herd. Elbow is generally considered an advanced dive because of the strong currents, which sweep you toward the deep water beyond the reef.
Though it's most famous for its spectacular wall dives, the atoll has dives for every level. The leeward side, where the reef is wide and gently sloping, is good for shallower dives and snorkeling; you'll see large concentrations of tube sponges, soft corals such as forked sea feathers and sea fans, and plenty of fish. Also on the atoll's western side is the wreck of the Sayonara. No doubloons to scoop up here—it was a small passenger and cargo boat that sank in 1985—but it's good for wreck dive practice.
Fishing here, as at all of the atolls, is world-class. You can fly-fish for bonefish and permit in the grassy flats, or go after migratory tarpon from May to September in the channels and lagoons of the atoll. Jack, barracuda, and snappers lurk in the mangrove-lined bays and shorelines. Billfish, sailfish, and other big creatures are in the blue water around the atoll.