Mayan ruins tower over the sea in Tulum. The formerly walled city was one of the last to be built by the Mayans, and its archaeological sites are incredibly well preserved. Take a break from the beach to visit El Castillo, the Temple of the Frescoes, and the Temple of the Descending God. Explore an underground river under a canopy of stalactites in the sacred caverns of LabnaHa Eco Park, or dive into Cenote Dos Ojos to snorkel inside of caves in the middle of a forest.