Cozumel

Four decades ago, Cozumel, Mexico's largest island, was a quiet fishing hamlet that received only a handful of visitors each year. Today it's one of the world's top diving destinations – thanks in part to Jacques Cousteau, who introduced the local reefs to the diving world.

More than 70 dive shops cater to those who come to enjoy the myriad reefs (including renowned Palancar, which lies just offshore), the more than 200 species of fish that inhabit them, and visibility of up to 100 feet. Not to mention the island's amazing water-filled caves called cenotes.

From April through August, when you're not looking through a face mask, you can fish for marlin and sailfish. The white-sand beaches are magnificent, and the most popular strands front the hotels and the calm waters of the island's west side. In summer, biologists from Cozumel's museum lead tours to watch sea turtles lay eggs on the secluded eastern shore. And just an 11-mile ferry hop away lies the Yucatán peninsula, gateway to the spectacular Mayan ruins at Tulum and Chichen Itzá.