Cozumel
The west-coast beaches of Cozumel. Photo via Wikimedia Commons.
Mexico's largest Caribbean island, just off Playa del Carmen, famous for the Palancar Reef and world-class drift diving in clear, calm water. The east side is wild and windswept, with beach bars and blowholes, while the town of San Miguel keeps a low-key island rhythm. Cruise ships dock here, but the water is the real draw.