Cenotes are natural pools of water, usually on the peninsula with limestone sedimentary rock floors, that have, over time, been filled with groundwater and rainwater, which are cool and clear. There are cave-type or open-air cenotes, which are formed when a cave collapses in on itself and can be open-air cenotes (the roof has completely collapsed) or cave cenotes (most or all of the roof remains). Many cenotes are home to various fish, plants, and even turtles. Throughout the Yucatan Peninsula, thousands of cenotes have become popular places for locals and travelers to cool off from the jungle heat. These are the best cenotes in Playa del Carmen, Tulum, Cancun, and Valladolid.