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.

바버렛츠 (The Barberettes) – Barbara Ann (Cover of The Beach Boys). The Barberettes is a South Korean retro, doo-wop female group that debuted in 2014 as a trio, and is based in Seoul.

Australian basketball player Liz Cambage poses during a portait shoot at Brighton Beach on March 29, 2011 in Melbourne, Australia.

Buddhist monks pray at Borobudur temple on Vesak Day, commonly known as “Buddha's birthday”, at the Borobudur Mahayana Buddhist monument on May 17, 2011 in Magelang, Indonesia. (Photo by Ulet Ifansasti/Getty Images)

Battersea Power Station. The chimney rims are thinner on top than you might expect. (Photo by Bradley L. Garrett)

A competitor shows her tattoos at the MBK Tattoo Contest in a shopping mall in Bangkok October 23, 2014. (Photo by Athit Perawongmetha/Reuters)

“Mother and Child”. Snow monkey at “Jigokudani hot-spring” in Nagano, Japan. (Photo by Kiyoshi Ookawa)