The Soyuz MS-17 spacecraft carrying the crew formed of Kathleen Rubins of NASA, Sergey Ryzhikov and Sergey Kud-Sverchkov of the Russian space agency Roscosmos blasts off to the International Space Station (ISS) from the launchpad at the Baikonur Cosmodrome, Kazakhstan on October 14, 2020. (Photo by Russian space agency Roscosmos/Handout via Reuters)

A woman drives a scooter with her dog in Hanoi on December 10, 2021, as Vietnamese officials in the central city of Hoi An announced it was set to be the country's first dog and cat meat free city. (Photo by Nhac Nguyen/AFP Photo)

Jordan Mann (R) falls into the water as he and Jordan Cross compete in the first round of Men's 3000 Meters Steeplechase during day four of the 2020 U.S. Olympic Track & Field Team Trials at Hayward Field on June 21, 2021 in Eugene, Oregon. (Photo by Patrick Smith/Getty Images)

A laborer is transporting used oil durms by a hand-pulled vehicle near Buriganga River in Dhaka on June 12, 2021. (Photo by Md Rakibul Hasan/ZUMA Wire/Rex Features/Shutterstock)

Mariana Sousa, student of the Ballet Paraisopolis, warms up during a rehearse in Paraisopolis favela, outskirts of Sao Paulo, Brazil on August 27, 2020, amid the new coronavirus COVID-19 pandemic. The 200 ballet students of Paraisopolis, the second largest favela in Sao Paulo, restarted rehearsals after five months with a coreography about a police operation that put their community in mourning last year. (Photo by Nelson Almeida/AFP Photo)

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.

Model Alba Carrillo attends “Glamour” beauty awards 2012 at Pacha Club on March 14, 2012 in Madrid, Spain. (Photo by Carlos Alvarez/Getty Images)