An exotic model poses for photographs at a news conference to promote the “Expo Sеx and Eroticism” adult exhibition in Mexico City, Mexico March 1, 2017. (Photo by Carlos Jasso/Reuters)

A competitor shows her nails during the Tokyo Nail Expo 2009 at Tokyo Big Sight on November 30, 2009 in Tokyo, Japan. (Photo by Junko Kimura/Getty Images)

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.

Migrants ride on top of a northern bound train toward the US-Mexico border in Juchitan, southern Mexico, Monday, April 29, 2013. Migrants crossing Mexico to get to the U.S. have increasingly become targets of criminal gangs who kidnap them to obtain ransom money. (Photo by Eduardo Verdugo/AP Photo)

A visitor tries a baccarat game at the Global Gaming Expo (G2E) Asia in Macau, China May 19, 2015. (Photo by Bobby Yip/Reuters)

A s*x worker (C) stages a performance to denounce what they say is abuse and social stigma against them in Madrid, Spain, October 14, 2015. Placard reads "Prostitutes are the ones that make the streets dirty". (Photo by Andrea Comas/Reuters)

Chen interacts with his “smart” sеx doll as he lays in a bed in his home in Guangzhou, Guandong Province, China, 05 April 2018. Chen, because of his busy pharmaceutical sales job and the travel it involves, has no time for a girlfriend. Chinese girls all want to talk about marriage after the second date and he is not interested in that for now, he said. (Photo by Aleksandar Plavevski/EPA/EFE)

A worker assembles a sеx doll at the WMDOLL factory in Zhongshan, Guangdong Province, China, July 11, 2018. The factory has over 200 full-time workers, all dolls are handmade and each requires the cooperation of at least five workers. (Photo by Aly Song/Reuters)