The Maya believed that cenotes were portals to the underworld. These mystical sites are ancient limestone sinkholes with crystal clear waters that are perfect for a unique freshwater diving experience. There are more than 6,000 cenotes in the Yucatan Peninsula. More advanced cave divers can explore the hundreds of kilometers of subway rivers in the area. The two most important departure ports for diving trips are Cancun and Playa del Carmen. You can also decide to explore only the sinkhole area of the cenote, which requires you to have an Open Water certification. Be aware that some of the cenotes may require divers to walk long distances through the jungle, which is an adventure in itself. Diving in Mexico's cenotes is definitely an awesome experience.