Choose to dive, snorkel or swim in the gem-colored waters near Tulum on Mexico's Caribbean coast. More than 6,000 natural limestone sinkholes, some with large pools, others, small and sheltered, once provided fresh water for the Mayan people and were considered portals to the gods. In fact, the word "cenote" means sacred well. Today, visitors can explore the craggy depths surrounded by colorful fish and turtles or swim on the surface, relishing the clear water that has been filtered by the earth. Some cenotes, such as the Gran Cenote of Tulum, are popular with tourists. Others are more remote and frequented by locals. Ask your hotel concierge or fellow travelers to find one that suits your style and interests.