A girl plays with colourful papers at the 23rd Sziget (Island) Festival on Shipyard Island in Budapest, Hungary, 13 August 2015. The festival is one of the biggest cultural events of Europe, offering art exhibitions, theatrical and circus performances and music concerts. Almost 200 performers from 47 countries will entertain the hundreds of thousands of visitors from 11 to 18 August. (Photo by Balazs Mohai/EPA)

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.

An Egyptian Coptic Christian girl carries palm decoration during Palm Sunday inside a church in Old Cairo, Egypt, April 5, 2015. For Christians worldwide, Palm Sunday marks Jesus Christ's entrance into Jerusalem, when his followers laid palm branches in his path, prior to his crucifixion. Western Christian churches and most Orthodox Christian churches follow different calendars and observe Easter on different dates. (Photo by Asmaa Waguih/Reuters)

A donkey is seen before the start of the procession of the “Virgem da Atalaia” during Holy Week at Alcochete, near Lisbon April 5, 2015. Women ride donkeys during the “Virgem da Atalaia” procession, that has been held annually for about 400 years. In the past, only single women rode the donkeys to ask for help from the Virgin to find a husband. (Photo by Rafael Marchante/Reuters)

Brazil's tallest teen is set marry her beau – despite him being over a foot smaller than her. Elisany da Cruz Silva (18) is a staggering 6ft 8ins (206 cm) tall while her compact fiancee Francinaldo da Silva Carvalho is only 5ft 4ins (162 cm). Despite a massive 1ft 4ins between them, Francinaldo had no problem increasing the distance by dropping to one knee after a romantic stroll along the beach. (Photo by Barcroft Media)

Residents (R to L) Luiza, Janubie, Leiticia and Lucas sit beneath an overpass near their houses in an impoverished area in the unpacified Complexo da Mare slum complex, one of the largest “favela” complexes in Rio, on March 18, 2014 in Rio de Janeiro, Brazil. (Photo by Mario Tama/Getty Images)

Ukraine's Olga Polyuk falls while competing in the freestyle skiing women's aerials qualification during the Beijing 2022 Winter Olympic Games at the Genting Snow Park A & M Stadium in Zhangjiakou on February 14, 2022. (Photo by Marco Bertorello/AFP Photo)

A girl plays at the West Side Hallo Fest, a Halloween festival in Bucharest, Romania, Friday, October 27, 2023. Tens of thousands streamed last weekend to Bucharest's Angels' Island peninsula for what was the biggest Halloween festival in the Eastern European nation since the fall of Communism. (Photo by Vadim Ghirda/AP Photo)