United States Marine Corps Staff Sgt. Jason Itro yells at recruit Nancy Carbins January 15, 2003 after she grabbed another recruit in the pool in an attempt to stay afloat during swim training at the Combat Pool on Parris Island, SC. Under the watchful eyes of swim instructors, recruits are required to swim in full gear and learn limited strokes and breathing to stay afloat. Carbins broke a major rule by grabbing another recruit and submerging them both. (Photo by Stephen Morton/Getty Images)

Visitors to Salisbury Cathedral stop to look at Sean Henry's sculpture Standing Man (2007) currently being exhibited in the Cloisters on August 2, 2011 in Salisbury, United Kingdom. The exhibition, “Conflux: A Union of the Sacred and the Anonymous”, features over 20 contemporary sculptures of dramatically different scales occupying vacant plinths and open spaces on both the inside and exterior of the iconic 13th century building. This exhibition brings to the Cathedral the biggest single group of polychrome sculpture since the Reformation and runs until the end of October. (Photo by Matt Cardy/Getty Images)

These images of abandoned hospitals across Italy are not for the faint-hearted. Both of the hospitals featured in the photographs are Italian asylums – known as manicomios – that were used as mental hospitals. Shut down by law in 1978, the derelict buildings are visibly overgrown and make for very eerie portraits. Photographer Thomas Windisch, 32, of Graz, Austria, said the asylums, located in top-secret spots, can get very creepy when there aren't many people there with him. Here: a hallway within an abandoned hospital. (Photo by Thomas Windisch/Caters News)

A supercell that spawned a tornado earlier makes it was east north of McLean, Texas on April 16, 2015 in Texas, United States. Huge hail, terrifying lighting and giant supercells the size of buildings – these incredible images depict a year in the life of a storm chaser. Shot in 2015 by photographer Mike Olbinski, 40, this series of pictures show both the beautiful and the extreme nature of weather in the United States. (Photo by Mike Olbinski/Barcroft Media)

Volunteers wearing face masks, gloves and protective gear to protect against coronavirus, gather to clean an area of an outdoor book market set up at Red Square with GUM, State Department store, left, St. Basil's Cathedral, center, Spasskaya Tower, second with, and the Kremlin Wall, right, in Moscow, Russia, Saturday, June 6, 2020. Muscovites clad in face masks and gloves ventured into Red Square for an outdoor book market, a small sign of the Russian capital's gradual efforts to open up amid coronavirus concerns. (Photo by Alexander Zemlianichenko/AP Photo)

A couple have taken their love of animals to the extreme – by opening up their home to over 100 rescued animals. Dr Prakash Amte and his wife, Dr. Mandakini Amte have dedicated their lives to helping both the animals – and people – of Hemalkasa, Maharashtra in India. Here: Prakash Amte is seen playing with a Hyena from his orphanage on September 19, 2017 in Maharashtra, India. (Photo by Haziq Qadri/Barcroft Media)

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.

An Amur tiger walks across a passageway after a news conference at the Philadelphia Zoo, Wednesday, May 7, 2014, in Philadelphia. The see-through mesh pathway called Big Cat Crossing is part of a national trend called animal rotation that zoos use to enrich the experience of both creatures and guests. (Photo by Matt Slocum/AP Photo)