A Definitive Ranking of the Top 10 Sights in the World

Second place in our list goes to a natural wonder stretching for more than 3,000 kilometers up the northeastern coast of Australia. The Great Barrier Reef hardly needs an introduction. But here are some facts: this is the world’s largest network of coral reefs, with 400 types of coral and 1,500 species of fish. Some 30 kinds of whales, dolphins, and porpoises have been spotted here, along with six species of sea turtles and 17 kinds of sea snake.

The reef is under threat from rising sea temperatures, but for now it's a psychedelic underwater playground for divers and snorkelers.