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 gory fight to the death between snarling dogs and captured wild boars. Gathered around a bamboo-walled arena, Indonesians in this remote part of Java island seem eager to watch the blood-curdling contests, known locally as “adu bagong” (boar fighting). Not surprisingly, animal rights activists are up in arms against the regular spectacle, which began in the 1960s when wild pig numbers in this area in West Java soared and they were hunted to protect crops. Here: Women share a joke as they walk to a paddy field in Cikawao village of Majalaya, West Java province, Indonesia, October 12, 2017. (Photo by Reuters/Beawiharta)

People walk past part of an outdoor display as preparations continue for the upcoming pop culture convention Comic Con in San Diego, California, U.S., July 17, 2018. (Photo by Mike Blake/Reuters)

England fan stripped down to her underwear and jumped in the canal in Birmingham, United Kingdom after team lose the 2018 World Cup semi- final against Croatia in Moscow on July 11, 2018. (Photo by Caters News Agency)

A man passes at the displayed art installation “Middle way” by Romanian artist Bogdan Rata in Kiev, Ukraine, Tuesday, November 20, 2018. The monument set on the central Kiev street of Khreshchatyk, at the place of Vladimir Lenin monument which was destroyed in 2013 during the Maidan events. (Photo by Efrem Lukatsky/AP Photo)

A man looks at a car hit by a post after a tornado ripped through a neighbourhood in Havana, Cuba on January 28, 2019. (Photo by Fernando Medina/Reuters)

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 woman throws water at passing motorists during celebrations for the Thingyan festival, also known as the Buddhist New Year, in Naypyidaw, Myanmar on April 16, 2019. (Photo by Thet Aung/AFP Photo)