QUINTANA ROO - SEPTEMBER 27: A scuba diver swims through rays of light coming into a massive underground, underwater cave in the Cenote Taj Maha in Quintana Roo, Mexico on September 27, 2018. Cenotes are massive sinkholes formed when the ceiling of a cave collapses underwater, creating a network of underwater caverns in crystal clear water that divers come from around the world to explore. In ancient times, cenotes served as the Mayan civilizations only source of water and were also held as being sacred to the Mayan People. They believed that the sinkholes represented a passage to the underworld, or "Xibalba in the Mayan language. Archaeologists have found fossils of mammoths, massive jaguars, and sloths in these underground cave systems, as well as human bones indicating ritual sacrifice and human presence in the cenotes as far back as 9,000 years ago. (Photo by Donald Miralle/Getty Images for Lumix)