People wash in water from a broken water pipeline on the outskirts of Kolkata, India, March 30, 2016. (Photo by Rupak De Chowdhuri/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.

A tourist splashes water on the frozen Songhua River on December 18, 2023 in Harbin, Heilongjiang Province of China. The water immediately freezes into ice in the frigid air. (Photo by VCG/VCG via Getty Images)

A bucket of water is splashed on a woman during the Songkran water festival to celebrate the Thai New Year, in Prachinburi Province, Thailand, April 13, 2024. (Photo by Wason Wanichakorn/AP Photo)

“Adventurers have gone deep underground to discover previously unexplored caves in these pictures. The awe-inspiring snaps show the cavers dwarfed by the huge series natural rock chambers in the Leye – Fengshan Geopark, China. Belgian photographer Francois-Xavier De Ruydts, 33, captured the team of explorers as they trekked through the deep wonderground in January 2014”. – Caters News. Here: Caving expedition in Fengshan, China, Guangxi province. (Photo by Francois-Xavier De Ruydts/Caters News)

“I’d come to the Altai Mountains on an Adventure Sherpas tour. Our group of 12 was made up mostly of Minnesotans who’d left warm weather and falling leaves for frosty Mongolia. We’d come to sleep in cozy ger tents, the traditional yurt abode of the Mongolian steppe; sip mare’s milk tea; climb mountain glaciers; ride horses to an ancient battle site, and attend the annual Eagle Hunting Festival in Ölgiy...”. – Kathryn Kysar via The Star Tribune. Here: hunter Berek and his eagle outside his home. (Photo by Brad Ruoho/The Star Tribune)

A woman sits on a terrace at Tiki hostel in Cantagalo favela, in Rio de Janeiro, Brazil, April 16, 2016. Hostels in a few of Rio's more than 1,000 slums serve not only as a cheap housing alternative for the more adventurous among the estimated 500,000 foreign tourists expected to arrive for the Olympics in August. The establishments also open up the rich culture of the city's shantytowns for travellers, giving them a glimpse into once “no-go” areas where about one-fifth of Rio's population lives. (Photo by Pilar Olivares/Reuters)

Here are the bravest of the brave in 2016. Weve gathered some of the finest images showing daredevils taking their lives into their own hands and going to the very brink this year. Whether they are perched hundreds of feet up on a high wire, courageously clinging to a rockface or taking on a volcano, these adventurers take the breath away. Here: Morgane Choquet and Samuel Cobb relax in a vertical campsite on the slopes of El Capitan, Yosemite National Park. (Photo by Alexandre Eggermont/Caters News)