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.

A tattoo of Captain America drawn by artist Sean Karon on the leg of client Ron Raucci at the Hampton Roads Tattoo Festival in Virginia, on March 2, 2012. The tattoo was completed from start to finish in one five-and-a-half hour session and won the prestigious “tattoo of the day” contest. (Photo by Jason Reed/Reuters)

Havilland Mosquito KA 114 performs a low pass during an airshow commemorating the completion of its rebuild on September 29, 2012 in Ardmore, New Zealand. The plane was restored by Warbird Restorations at Ardmore Aerodrome and is the only flying Mosquito in the world. (Photo by Simon Watts)

In this image released on December 9, 2021, evian today announced that British tennis star Emma Raducanu will be the brand’s new Global Ambassador. Emma is the latest tennis icon to join the evian family. Emma has been hailed as an inspiration to young tennis players across the globe and a rising star both on and off court. (Photo by Julian Finney/Getty Images for evian)

Former Division I volleyball star Kayla Simmons in the second decade of July 2023 wowed her fans in a stunning bikini snap on social media. Kayla has been called the world's sexiest volleyball star. (Photo by @kaylasimmmons/Instagram)

Former Coronation Street star Helen Flanagan was the subject of more mum shaming as she posts eye-popping snap. The I'm A Celeb: South Africa star took to social media with a risque snap as she enjoyed a London getaway in the first decade of September 2023. (Photo by @hjgflanagan/Instagram)

A Thorneycroft motor van as used during World War I. (Photo by Topical Press Agency/Getty Images). August 1914

p*rn star Asa Akira models the Namilia collection at Pier 59 Studios during NYFW Fall/Winter 2020 on Sunday, February 9, 2020 in New York. (Photo by Charles Sykes/Invision/AP Photo)