Enthusiasts gathered at Cad East in Snowdonia National Park, England to take pictures of F-15 Eagle fighters as they completed the Mach Loop, November 2017. (Photo by Caters News Agency)

An employee stands on the step of The Venice Simplon-Orient-Express at Istanbul Station in Istanbul, on August 31, 2022. The Venice Simplon Orient-Express luxury train arrives in Istanbul, completing its annual voyage along a mythical route that takes it across Europe from Paris. (Photo by Yasin Akgul/AFP Photo)

Havilland Mosquito KA 114 performs a low pass during an airshow commemorating the completion of its rebuild on September 29, 2012 in Ardmore, New Zealand. The plane was restored by Warbird Restorations at Ardmore Aerodrome and is the only flying Mosquito in the world. (Photo by Simon Watts)

A tattoo of Captain America drawn by artist Sean Karon on the leg of client Ron Raucci at the Hampton Roads Tattoo Festival in Virginia, on March 2, 2012. The tattoo was completed from start to finish in one five-and-a-half hour session and won the prestigious “tattoo of the day” contest. (Photo by Jason Reed/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.

These talented turtles have been "snapped" performing for the camera as they practice their synchronized swimming routine. Photographed underwater by Monste Grillo, 36, from Tenerife, Spain, the turtles are seen swimming in unison as well as touching fins as they circle towards the surface. After spending hours in the water off the coast of the Canary Islands in 2012, the photographs capture the gentle nature of the creatures as well as giving a fascinating glimpse into their behavior in the wild. (CATERS NEWS)

Workers put some finishing touches on “Forever Marilyn”, a sculpture by Seward Johnson, on July 14, 2011 in Chicago, Illinois. The stainless steel and aluminum sculpture which stands 26 feet tall and weighs 34,000 pounds will be unveiled tomorrow and remain on display in Chicago through the spring of 2012. The sculpture was inspired by Marilyn Monroe's iconic scene in the 1955 movie “Seven Year Itch”. (Photo by Scott Olson/Getty Images)

A Chinese girl touches the gun of a relievo featuring Chinese soldiers fighting with Japanese troops during World War II at an exhibition at the Anti-Japan War Museum to mark the 60th Anniversary of the Victory of the Chinese People's War of Resistance Against Japan on August 18, 2005 in Beijing, China. (Photo by Cancan Chu/Getty Images)