A man holds a child after rescuing him from a kindergarten affected by a fire at a commercial building, in Ningde, Fujian province, China, September 16, 2015. According to local media, more than 260 people were evacuated due to the fire, which broke out Wednesday morning. No causalities have been reported and the cause of it is still unknown. (Photo by Reuters/China Daily)

With the city of Miami skyline behind it a grand piano is seen on a sandbar in Biscayne Bay on January 26, 2011 in Miami, Florida. It's unknown how or why the heavy musical instrument was on the sandbar but some were speculating it was part of a music video production. The piano was charred from being burned. (Photo by Joe Raedle/Getty Images)

The main entrance and blast door at the nuclear bunker site on the Woodside Road industrial estate on February 4, 2016 in Ballymena, Northern Ireland. The underground shelter has been put up for sale by the offices of the Northern Ireland First and Deputy First Minister. The bunker which was completed in 1990 was built to hold up to 235 people in the event of a nuclear bomb and is complete with kitchen facilities, dormitories and decontamination chambers. The site, one of approximately 1,600 nuclear monitoring posts built in the UK since 1955, is on the housing market with an asking price of £575,000. (Photo by Charles McQuillan/Getty Images)

LA-based photographer Mike Kelley has been working on his amazing “Airportaits” for two years. He racked up racked up more than 74,000 air miles on 25 flights to complete the series. (Photo by Mike Kelley/SWINS)

Construction work on the tower began in November 2008. Upon its completion this year the building will stand approximately 632 meters (2,073 ft.) high and will have 121 stories. It is expected to open to the public in 2015. (Photo by Rex Features)

An adult female Masai giraffe rears on its hind legs as it resists efforts by Kenya Wildlife Services (KWS) rangers to guide it into a transportation crate using ropes during an exercise to translocate large herbivores from Kedong Ranch due to land subdivisions and corralling that have disrupted wildlife migratory routes in Naivasha, Nakuru County, on November 16, 2025. Driven by two long ropes held by about twenty rangers, the blindfolded giraffe enters a tall trailer that is to transport it out of its natural habitat in the Rift Valley, which is deteriorating after having been resold. This is the first step in a meticulous relocation operation in the vast Kedong ranch, part of an ancestral corridor between Mount Longonot and Hell's Gate Park, near the iconic Lake Naivasha. (Photo by Tony Karumba/AFP Photo)

Visitors walk past the fully equipped dining table inside the “Crazy House”, which is completely built upside-down, in the village of Affoldern near the Edersee lake, May 7, 2014. Three friends came up with the idea to build the tourist attraction, which cost about 200,000 euros and took some six weeks to complete. (Photo by Kai Pfaffenbach/Reuters)

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.