A grey seal basks under a rainbow on a beach on the Lincolnshire coast, England on November 21, 2017. (Photo by Sean Weekly/Caters News Agency)

Pakistani truck drivers from different cities sit on the roof top of the buildings at Truck station offering Dua before breaking the fast during Holy month of Ramadan in Lahore on April 15, 2021. Ramadan is marked by daily fasting from dawn to sunset Islami's holy month of Ramadan-ul-Mubarak is celebrated by Muslims worldwide marked by fasting, abstaining from foods, sеx and smoking from dawn to dusk for soul cleansing and strengthening the spiritual bond between them and the Almighty. (Photo by Rana Sajid Hussain/Pacific Press/Rex Features/Shutterstock)

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.

To an outsider, their passion is at times illegal and often on the verge of life and death. But climbing rooftops of high-rise buildings and exploring abandoned facilities is in the blood of these young Muscovites. The small group calls itself “Rudex”, which stands for “roof and decay exploration”, and is akin a Western youth craze known as urbex or “urban exploration” of man-made structures. Here: Urban explorer Vad Him of Rudex team jumps whilst on a rooftop in Moscow, Russia, August 14, 2017. (Photo by Maxim Shemetov/Reuters)

Stunning images have revealed ice-cool British tourists chilling out inside Europe’s largest glacier – despite being at risk of flooding. The spectacular collection of images show the explorers braving the freezing temperatures to climb, photograph and even abseil down the inside of the icy cliff sides. Another image shows one visitor on his knees appearing to pray next to a water fall of melted ice. Other glistening shots show an adventurer trying to keep warm by a fire whose flames dance beautifully against the glossy roof. (Photo by Einar Runar Sigurdsson/Mediadrumworld.com)

World Champion Trials bike rider Jack Field of Australia poses after performing the highest backflip on a motorcycle ever recorded as he flips his motorbike upside down on the roof of Melbourne's Eureka Tower (297.3 metres) during a AUS-X Open media opportunity at Eureka Tower on May 22, 2019 in Melbourne, Australia. The largest international Supercross and action sports event in the world outside of the USA, the AUS-X Open will be held at Melbourne's Marvel Stadium on November 30 2019. (Photo by Scott Barbour/Getty Images)

Germany, Business couple making love under desk. (Photo by Roman Maerzinger/Getty Images)

A child sleeps under a table at the Jorkpan market in Sinkor district in Monrovia, Liberia on May 2, 2016. (Photo by Marco Longari/AFP Photo)