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)

Dancers from the Yarrabah community perform during the Laura Aboriginal Dance Festival on June 18, 2011 in Laura, Australia. The Laura Aboriginal Dance Festival is a celebration of aboriginal dance and culture that takes place Biennially in Cape York Peninsula at the site of a traditional Bora ground that is sacred to the aboriginal community and surrounded by some of the oldest rock art in the world. Over 5000 visitors attend the festival, offering a unique insight into the community and providing an opportunity to spread cultural traditions to new generations. The festival takes place June 17-19. (Photo by Mark Kolbe/Getty Images for Tourism Queensland)

Kendall Jenner uses her cellular device during Kanye West's Yeezy Season 3 Collection presentation and listening party for the “The Life of Pablo” album during New York Fashion Week February 11, 2016. (Photo by Andrew Kelly/Reuters)

Dancers of the Czech National Ballet warm up backstage during a performance of “The Nutcracker – A Christmas Carol” at the National Theatre in Prague, Czech Republic, late 16 December 2017. Peter I. Tchaikovsky's “The Nutcracker”, one of his most famous compositions and seasonal ballets, premiered in St. Petersburg, Russia, on 18 December 1872, celebrates its 125th anniversary this year. (Photo by Martin Divisek/EPA/EFE)

Participants dance and climb on an art installation as approximately 70,000 people from all over the world gather for the 30th annual Burning Man arts and music festival in the Black Rock Desert of Nevada, U.S. August 31, 2016. (Photo by Jim Urquhart/Reuters)

People take cover outside the Fort Lauderdale-Hollywood International airport after a shooting took place near the baggage claim on January 6, 2017 in Fort Lauderdale, Florida. Officials are reporting that five people were killed and 8 wounded in an attack by a single gunman. (Photo by Joe Raedle/Getty Images)

Caterine Ibarguen of Team Colombia competes in the Women's Triple Jump Qualification on day seven of the Tokyo 2020 Olympic Games at Olympic Stadium on July 30, 2021 in Tokyo, Japan. (Photo by Matthias Hangst/Getty Images)