Tourists pose for photos at the Skybox at Kuala Lumpur Tower in Kuala Lumpur, Malaysia, Wednesday, July 1, 2020. Malaysia entered the Recovery Movement Control Order (RMCO) after three months of coronavirus restrictions. (Photo by Vincent Thian/AP Photo)

Mexican training ship “Cuauhtemoc” moves past the Galata Tower in Istanbul, Turkiye on July 18, 2023. “Cuauhtemoc”, which was sent by the Mexican government as a sign of friendship between the two countries on the occasion of the 100th anniversary of the founding of the Republic of Turkiye, arrived at Sarayburnu Port. (Photo by Omer Faruk Yildiz/Anadolu Agency via Getty Images)

The sun rises this morning behind the 173ft spire of St Mary's church in the market town of Whittlesey in Cambridgeshire, UK on February 17, 2024. The church dates from the 13th century with the Ashlar faced tower added in the 15th century. (Photo by Andrew McCaren/London News Pictures)

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.

Lily Aldridge and Elsa Hosk take a selfie in front of the Eiffel Tower prior the 2016 Victoria's Secret Fashion Show on November 29, 2016 in Paris, France. (Photo by Dimitrios Kambouris/Getty Images for Victoria's Secret)

A detail of the Sagrada Familia Basilica, designed by architect Antoni Gaudi, in Barcelona, Spain, Wednesday, October 21, 2015. Barcelona's breathtaking La Sagrada Familia Basilica has begun its final phase of raising six immense towers. Presenting the project Thursday, chief architect Jordi Fauli said the central "Tower of Jesus Christ," the tallest of the six, will rise 172.5 meters (566 feet) high, making it "the tallest religious building in Europe". (Photo by Manu Fernandez/AP Photo)

Artist German Vinogradov acts in the performance of the burning of Maslenitsa tower, devoted to Pancake Week, a pagan holiday marking the end of winter, in the village of Nikola-Lenivets, Kaluga region, Russia, February 25, 2017. (Photo by Maxim Shemetov/Reuters)

A ballet dancer attends a photo shooting as activists from the environmentalist group Greenpeace unfurl a giant banner on the Eiffel Tower which reads “Liberty, Equality, Fraternity” in a call on French citizens to vote against the National Front (FN) presidential candidate Marine Le Pen, in Paris, France May 5, 2017. (Photo by Gonzalo Fuentes/Reuters)