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.

In this Thursday, February 19, 2015 photo, participants at a seminar on edible insects taste a Cricket Consomme at Le Cordon Bleu cooking school in Bangkok, Thailand. A group of chefs and food scientists at the esteemed French school's branch in Bangkok spent the week simmering, sautéing and grilling insects to extract innovative flavors they say could open a new frontier for the world of gastronomy. (Photo by Sakchai Lalit/AP Photo)

Dead sperm whales are seen washed up on a beach on Texel Island, The Netherlands, January 13, 2016. The five sperm whales that beached on the Dutch lsland of Texel on Tuesday have died overnight, Dutch media reported. It is extremely unusual for so many whales to be in Dutch waters, a spokesman for the Ecomare marine centre told local paper Noordhollands Dagblad. Efforts to get the whales back into open water on Tuesday evening failed and rescuers finally withdrew from the beach at around midnight. The area of beach where the whales are has been closed to the public, to minimise the distress to the animals. (Photo by Cris Toala Olivares/Reuters)

Renee LeGrand, of Foothill Ranch, Calif., takes a picture among wildflowers in bloom Monday, March 18, 2019, in Lake Elsinore, Calif. About 150,000 people flocked over the weekend to see this year's rain-fed flaming orange patches of poppies lighting up the hillsides near Lake Elsinore, a city of about 60,000 residents. The crowds became so bad Sunday that Lake Elsinore officials closed access to poppy-blanketed Walker Canyon. By Monday the #poppyshutdown announced by the city on Twitter was over and the road to the canyon was re-opened. (Photo by Gregory Bull/AP Photo)

A common kingfisher sits on a branch of a tree after catching an insect in Allahabad, India, Sunday, July 9, 2017. The common kingfisher is a highly territorial bird that has to eat nearly sixty percent of its bodyweight every day. (Photo by Rajesh Kumar Singh/AP Photo)

A white-throated kingfisher (Halcyon smyrnensis) sits over a tree in a field in Lahore, Pakistan, 26 March 2021. The most familiar Kingfisher species can be observed perched on branches or walls while on the lookout for grubs, insects and even fish in streams or garden ponds. (Photo by Rahat Dar/EPA/EFE)

Now celebrating its 40th year, Nikon Small World is widely regarded as the leading forum to recognize proficiency and photographic excellence of photography taken under the microscope. To select the winners, competition judges analyzed entries from all over the world covering subjects ranging from chemical compounds to up-close-and-personal looks at biological specimens. The 2014 winners will be revealed on October 30th. In 2014, the competition received over 1,200 entries from more than 79 countries around the world. (Photo by Dr. Igor Robert Siwanowicz/Nikon Small World 2014)

Rascal, and her brother Petey, were abandoned as pups near the railroad tracks in Union County, Arkansas. She is a pit bull cross and approximately 6 months old, in Arkansas, United States. These canine portraits will make any dog lover's day – and they're helping to get sheltered pups adopted at the same time. Kind-hearted photographer Tammy Swarek came up with the idea of dressing up rescue dogs to draw attention to their stories and help potential owners personally connect with them. (Photo by Tammy Swarek/Barcroft Images)