A participant wearing Kokoshnik, the Russian traditional headwear, walks out of the water during winter swimming festival in the town of Podolsk, south of Moscow, Russia January 5, 2017. (Photo by Maxim Shemetov/Reuters)

English singer-songwriter, dancer, model and actress Sarah Harding attends the launch of Walkers Bring It Back Campaign at Vinopolis on September 3, 2015 in London, England. (Photo by Joseph Okpako/WireImage)

A model presents a creation from the LaQuan Smith Fall and Winter '23 collection at the Rainbow Room during Fashion Week in New York City, New York, U.S., February 13, 2023. (Photo by Caitlin Ochs/Reuters)

Competitors drive their homemade vehicle without an engine during the Red Bull Soapbox Race in Almaty, Kazakhstan on September 11, 2022. (Photo by Pavel Mikheyev/Reuters)

Mongolian Chinese performs a traditional Chinese dance in front of the Olympic Rings located near the National Stadium, the main stadium for the 2020 Tokyo Olympic Games in Tokyo, Japan July 29 2021. (Photo by Androniki Christodoulou/Reuters)

People enjoying the second day of the Greenman Festival in South Wales, Crickhowell, United Kingdom on August 20, 2021. (Photo by Chris Fairweather/Huw Evans/Rex Features/Shutterstock)

A cenote is a natural phenomenon, a sinkhole in the Earth’s surface. The Yucatan Peninsula in Mexico has an estimated 7,000 cenotes because it is primarily made up of porous limestone. For millions of years, rainfall slowly ate away at the limestone and a huge system of underground caves and caverns was formed. Many filled with water from rain or from the underground water table. When the roof of a water filled cave collapses, a cenote is born. The water found in a cenote may be fresh water, salt water, or both. Structurally it may be completely open, like a lake, almost completely closed with just a small opening at the top, or somewhere in between.

Shephen Shine, 27, who lost a leg when serving in Iraq in 2007, is tattood with a regimental tattoo reading “Their Sacrifice – Our Freedom” during the Ink For Heroes event on June 18, 2011 in Catterick, England. Ink For Heroes is a charity event to raise money and awareness of the soldiers that get injured during service, with all proceeds going to both “Help The Heroes” and “The British Legion”. Injured soldiers can also get tattooed for free during the event. (Photo by Bethany Clarke/Getty Images)