Lisa Yu crawls through a mud pit under low slung barbed wire as she competes in The Tough Bloke Challenge on March 4, 2012 in Melbourne, Australia. The Tough Bloke Challenge is one of the most gruelling adventure runs in Australia consisting of 18 obstacles over a 6 km cross-country course laden with thick mud-pits and ice-cold water crossings. (Photo by Scott Barbour/Getty Images)

Without the use of any type of scuba equipment, divers descend to great depths armed with underwater guns, harpoons and strong line to stalk and hunt prey. Some of the best free-divers in the world can hold their breath for up to 5 minutes under water and go to depths greater than 100 feet.

(All photography © Eyeconic Images.)

A competitor scrambles in the mud under barbed wire during the Tough Guy Challenge 2009 at South Perton Farm on February 1, 2009 in Wolverhampton, England. The biannual event to raise cash for charity challenges thousands of international competitors to run through a gruelling set of 21 obstacles including water, fire and tunnels after a lengthy run at the start. (Photo by Christopher Furlong/Getty Images)

Handout picture released by Telam showing the tarmac of the Pedro Palacios Avenue in Ramos Mejia, province of Buenos Aires, Argentina, under which the channeled waters of the Maldonado stream flow, after it collapsed on April 8, 2014 leaving a 40-metre-long, 1.4-metre-deep hole. About 3000 people had to be evacuated in the Argentine provinces of Neuquen (soutwest), Catamarca (northwest), Santiago del estero (center) and Cordoba (center)due to the foods caused by heavy rain, official sources said. (Photo by Daniel Dabove/AFP Photo)

In this photo taken on Saturday, January 26, 2019 photo, rescued flamingo chicks have access to water at a centre after being rescued from a dried out dam in Kimberley, South Africa. A special airlift for thousands of baby flamingos is under way in South Africa as drought has put their breeding ground in peril. A reservoir that hosts one of southern Africa's largest flamingo populations is drying up. (Photo by AP Photo/Stringer)

Underwater photographer Sarah Lee uses a technique known as “duck diving” to capture these stunning photos of surfers in Hawaii. Surfers “duck dive” under the water to avoid incoming waves so they can get further out to sea. Photo: A surfer comes free from her surfboard. (Photo by Sarah Lee/Caters News)

Iraqi boys swim with a herd of buffaloes in the Diyala River in the Faziliah district, east of Baghdad on August 2, 2021, amid extreme summer temperatures. As Iraq bakes under a blistering summer heat wave, its hard-scrabble farmers and herders are battling severe water shortages that are killing their animals, fields and way of life. (Photo by Ahmad Al-Rubaye/AFP Photo)

This is the amazing moment a heroic hippo saved a gnu from certain death. After being bitten by a crocodile, the large antelope is seen being dragged slowly under the water. But in a miraculous turn of events, a nearby hippo is seen making its way across the water to help the animal in its hour of need. Photo: One of the biggest hippos protects the gnu as it makes its way back to the shoreline, guarding it from any further attacks. (Photo by Vadim Onishchenko/Caters News)