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.

Boys pose with their toy guns as others play on swings, on the first day of the Muslim holiday of Eid al-Fitr, which marks the end of the holy month of Ramadan, in the government-controlled district of Dwelaa in Damascus, Syria July 6, 2016. (Photo by Omar Sanadiki/Reuters)

A woman from the Hui Muslim community carries food that will be eaten by her and others to break their fast during the holy fasting month of Ramadan at the Nanxiapo Mosque on June 8, 2018 in Beijing, China. (Photo by Kevin Frayer/Getty Images)

These snaps show a pair of daredevil bikers performing gravity-defying stunts as they get covered from head to toe in brightly colored powder. The stunning action shots show the fearless duo perform nail-biting tricks on their BMX bikes as they get showered with the brilliantly colored powder. The amazing images were taken by Christoph Jorda, from Bavaria, Germany, with bikers Thomas Kaiser and Konstantin Ottner. Here: The biker with the holi powder behind whilst performing stunts. (Photo by Christoph Jorda/Caters News)

Penitent Jerry Mazon, 9, wears his “Morions” mask while playing with his baby brother during Holy Week celebrations in Mogpog, Marinduque in central Philippines March 22, 2016. (Photo by Erik De Castro/Reuters)

A Filipino flagellant crawls along a street on Maundy Thursday, in San Fernando city, Pampanga Province, north of Manila, Philippines, 24 March 2016. Many Filipino Catholic penitents mark the Holy Week by submitting to different forms of physical penance in the hopes of being forgiven for their sins. (Photo by Francis R. Malasig/EPA)

An effigy representing Judas Iscariot burns as some people wearing masks watch during Holy Week in the Catia neighborhood of Caracas, Venezuela, Sunday, April 4, 2021. The Burning of Judas is an Easter-time ritual in many communities, where an effigy of Judas Iscariot is hanged on Good Friday, then burned on Easter Sunday. (Photo by Matias Delacroix/AP Photo)

A Hindu holy man shouts religious slogans during a procession to mark 'Krishna Janmashtami' in Srinagar, Indian controlled Kashmir, Friday, August 19, 2022. Krishna Janmashtami marks the birth of Hindu god Krishna. (Photo by Mukhtar Khan/AP Photo)