A fisherman transports a dead whale shark after it was caught in fishermen's net, in Yangzhi county, Fujian province August 1, 2014. According to local media, the whale shark is five-metre-long and weighs over 2 tonnes. (Photo by Reuters/Stringer)

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 man playing the part of a zombi pretends to rise from the dead from inside a coffin at a Carnival parade in Jacmel, Haiti, Sunday, February 23, 2014. The pre-Lent festival began in the streets of this town known for its arts to kick off Haiti’s Carnival festivities. (Photo by Dieu Nalio Chery/AP Photo)

In this Sunday, February 18, 2018 photo, Palestinian camel herder Salem Rashaideh, leads the way for the camels in the territory of Israeli Kibbutz Kalya, near the Dead Sea in the West Bank. For three months a year, in the winter time Bedouin Arab herders take their 130 camels to graze on the shores of the Dead Sea, at the lowest place on Earth. (Phoro by Oded Balilty/AP Photo)

“The World Stands on its Head” (“Die Welt Steht Kopf”) House on the Baltic Sea Island of Usedom stands nearly completed on September 3, 2008 in Trassenheide, Germany. The upside down house, complete with upside down interior furnishings, is the brainchild of Klaudiusz Golos and Sebastian Mikiciuk, and will become a local tourist attraction. (Photo by Sean Gallup/Getty Images)

Enthusiasts gathered at Cad East in Snowdonia National Park, England to take pictures of F-15 Eagle fighters as they completed the Mach Loop, November 2017. (Photo by Caters News Agency)

The phenomenon of the Hill of Crosses in northern Lithuania began when people started leaving crosses there hundreds of years ago – and continues to this day. These photos of a hill covered in crosses show the amazing sight it has become. Photo: In 1831 an unsuccessful uprising against the Russian czar left many rebels dead. Relatives of the dead rebels, with no bodies to bury, instead left crosses, according to the Daily Mail. (Photo by Richard Gardner/Rex USA)

Two office workers wearing summer kimonos Yukata look at paper lanterns as they visit on the eve of Mitama Matsuri, a summer festival at Yasukuni Shrine in Tokyo, Japan, 13 July 2015. About 300,000 people visit the shrine decorated with about 30,000 lanterns during the three-day summer festival aiming at comforting souls of dead, especially for the war dead. The festival is after Japan's Buddhist custom to honor and comfort souls of family's ancestors. (Photo by Kimimasa Mayama/EPA)