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.

Miners search for jade stones at a mine dump at a Hpakant jade mine in Kachin state, Myanmar November 25, 2015. Using heavy earth-excavators and explosives, miners have been tearing into Myanmar's northern hills in recent months, in a rush to excavate more jade from the world's richest deposits of the gemstone before a new government takes office next year. (Photo by Soe Zeya Tun/Reuters)

In this artist's impression supplied by the ESO (European Southern Observatory) on April 25, 2007, the planetary system around the red dwarf, Gliese 581, is pictured showing what astronomers believe is the most earth like planet found outside our solar system to date. Using the ESO 3.6-m telescope in Chile, astronomers have uncovered the planet which could have water running on its surface. The planet orbits the faint star Gliese 581, which is 20.5 light-years away in the constellation Libra. (Photo by ESO via Getty Images)

A graffiti, portraying a woman, is seen in Medellin, Colombia on November 19, 2017. Mural graffitis from different artists, street art can be seen in almost every city on Earth, but street arts raw power and potential for change was felt by me most intensively in Medellins Comuna 13, previously one of Colombias most dangerous neighbourhoods, in fact Communa 13 was constant battleground between gangs, narcos, paramilitaries and the government, but today you would hardly recognise it. (Photo by Juancho Torres/Anadolu Agency/Getty Images)

Chocolate is the greatest gift the Earth has given us. The dessert table would be a sad sight without it. It’s so beloved, so appreciated, that the Swedish scientist who named the cocoa plant that gives us chocolate called it Theobroma cacao, which means “food of the gods”. Here: Farmer holding a freshly cut cocoa bean pod, revealing the pulp and seed inside on a rainforest farm. (Photo by Doug McKinlay/Getty Images)

“A team of expert cavers and photographers had been exploring caves in the Chongquing province of China – when they were amazed to discover the entrance to a hidden cave that was previously undiscovered. And they were stunned when they managed to enter the ginormous cave – and found that it was so large there was even a cloud inside it – a cave so large it has its own weather system. Photographer and caver Robbie Shone, from Manchester, was part of a team of 15 explorers on a month-long expedition who stumbled across the natural wonder”. – Caters News

A migrant holds a placard which reads “No Forced Deportations” as he rides his bicycle at the makeshift camp called “The New Jungle” in Calais, France, September 18, 2015. Around 3,500 migrants and refugees are camped in Calais, fleeing war and poverty in the Middle East, Africa and Asia and now living in the jungle. Most of them are hoping to make the crossing to England. (Photo by Regis Duvignau/Reuters)

An Israeli soldier watches as revellers take part in a gay pride parade in Tel Aviv, Israel, June 3, 2016. About 200,000 people from the LGBT community in Israel and abroad attended in Tel Aviv's annual gay pride parade Friday, the largest event of its kind in the Middle East. (Photo by Baz Ratner/Reuters)