A blue crab, a highly invasive alien species, is seen at Lio Piccolo during the reforestation day on April 05, 2025 in Venice, Italy. The island of Lio Piccolo in the northern lagoon of Venice is being replanted with 16,000 new trees that will protect the salt marsh ecosystem that is fundamental to the natural health of Venice and the lagoon by WOWnature project, an Etifor initiative. (Photo by Simone Padovani/Getty Images)

Entertainers from the She Huo cultural troupe rehearse for the Edinburgh Military Tattoo at Redford barracks on August 5, 2009 in Edinburgh, Scotland. (Photo by Jeff J Mitchell/Getty Images)

Dan McManus and his service dog Shadow hang glide together outside Salt Lake City, Utah, July 22, 2013. McManus suffers from anxiety and Shadow's presence and companionship help him to manage the symptoms. The two have been flying together for about nine years with a specially made harness for Shadow. (Photo by Jim Urquhart/Reuters)

In this picture taken on Thursday, December 1, 2016, an Iranian woman covers herself with a blanket due to the cold, while visiting Khour salt lake during her tour of the Mesr desert about 305 miles (500 kilometers) southeast of the capital Tehran, Iran. Deserts make up parts of Iran which have recently become tourist destination for young Iranians looking for a break on their weekend. The increase in tourists to the desert has stimulated economic growth in the area. (Photo by Ebrahim Noroozi/AP Photo)

Japanese artist Mami Kiyoshi has spent 15 years creating vivid portraits of people surrounded by their belongings – from wine bottles and violins to the odd stray pet. Mami Kiyoshi’s ongoing series “New Reading Portraits” is, in part, a nod to the mise-en-scène found in traditional woodcut printing. Here: Sakura and Kazuhiro, Tokyo, 2015. (Photo by Mami Kiyoshi/Galerie Annie Gabrielli/The Guardian)

“Be prepared” is the motto of petite Doris Sherrell, vocalist and dancer with “Blackouts of 1942”. In the event of a bombing, the young lady had her social security number tattooed on one leg by artist Jack Julian, and address placed on the other limb for means of identification in Los Angeles, September 29, 1942. (Photo by AP Photo)

A tattoo of the model who presents a creation by designer Maxime Simoens is seen in detail, as part of his Haute Couture Spring-Summer 2019 collection show for fashion house Azzaro Couture in Paris, France, January 21, 2019. (Photo by Gonzalo Fuentes/Reuters)

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.