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 fisherman caught a record-breaking 805lb Mako shark – and then barbecued and ate it with his friends. Joey Polk, 29, and his two cousins Earnie Polk, 43, and Kenny Peterson, 21, battled the 11ft predator for more than an hour before finally hauling it onto the beach. They normally tag and release their catches for conservation but were unable to resuscitate this one and instead made it the main course at a jumbo-sized family barbecue. (Photo by Joey Polk/Barcroft Media)

Arab Israeli contestant Tallinn Abu Hana poses for the judges during auditions for the first Miss Trans Israel beauty pageant in Tel Aviv, Israel, Thursday, March 3, 2016. The winner will represent Israel at a Miss Trans Star International pageant to be held in Spain in August. Tel Aviv has emerged as one of the world's most gay-friendly travel destinations, standing in sharp contrast to most of the rest of the Middle East, where gays can face persecution. (Photo by Ariel Schalit/AP Photo)

An old toilet is displayed during the “Toilet!? Human Waste and Earth's Future” exhibition at The National Museum of Emerging Science and Innovation – Miraikan on July 1, 2014 in Tokyo, Japan. The exhibition focuses on how the toilet has changed our daily lives and discovers what the most environment-friendly and ideal toilet is. (Photo by Keith Tsuji/Getty Images)

North Korean girls in similar bathing suits stand under a shower at the Songdowon International Children's Camp, Tuesday, July 29, 2014, in Wonsan, North Korea. The camp, which has been operating for nearly 30 years, was originally intended mainly to deepen relations with friendly countries in the Communist or non-aligned world. But officials say they are willing to accept youth from anywhere – even the United States. (Photo by Wong Maye-E/AP Photo)

Going nowhere in a hurry, this friendly Javan Tree frog can be seen casually hopping aboard the slow-paced snail who like a lonely highway trucker is only too happy to have the company. These cute critters chew the fat until froggy reaches his destination and alights at the top of the branch. Creative Designer and amateur photographer Kurit Afsheen (34) was able to capture this special sequence while out in his back garden in Ciledug, Indonesia. (Photo by Kurit Afsheen/Media Drum World)

In this Tuesday, September 12, 2017 photo, Amornrat Simapsaisan, a local shop manager, watches before she ate watermelon salad with bamboo worms, at Inspects in the Backyard restaurant, Bangkok, Thailand. Tucking into insects is nothing new in Thailand, where street vendors pushing carts of fried crickets and buttery silkworms have long fed locals and adventurous tourists alike. But bugs are now fine-dining at the Bangkok bistro aiming to revolutionize views of nature’s least-loved creatures and what you can do with them. She tucked in quite happily to her watermelon and cricket salad on a recent evening. “It’s tasty. It’s munchy”, she said. (Photo by Sakchai Lalit/AP Photo)

Participants run at the “Half-Naked Marathon” at Olympic Forest park in Beijing, China, February 28, 2016. This annual running event which requires participants to run half-naked, was organized to promote environmentally friendly lifestyles. (Photo by Kim Kyung-Hoon/Reuters)