Astrolabe Reef, Fiji
Credit: Casey Mahaney / Getty Images

One of the world's largest ribbon barrier reefs, Great Astrolabe Reef sits in 80-degree water so clear you can see straight to the bottom 82 feet below, where pillars of coral called bommies grow. Actually two reefs surrounding several islands, the largest of them Kadavu Island, the coral forms a protected lagoon perfect for snorkeling. Kadavu has no roads and only a few resorts, so there won't be tourist hordes scaring away the manta rays visiting cleaning stations or the clouds of colorful reef fish swimming beneath you. Giant clams, sea turtles, eels, sea horses, reef sharks, octopi and dolphins are common sights as well. Daily flights from Suva on the main island of Fiji serve Kadavu, after that you get around by foot or boat.