I'm sure you don't need me to tell you that climbing Everest is dangerous, but what about if you take a challenge like that and plunge it under more than 300 feet of water?
Doesn't sound very pleasant, does it? And yet some divers have risked taking on such a challenge at Eagle's Nest in Florida.
The cave, dubbed the 'Mount Everest' of the cave diving world, features on numerous lists about 'dangerous' and 'risky' places to visit, and is known to have claimed the lives of at least 13 people who have attempted to dive in it.
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The water doesn't look that inviting on the surface - in fact, it looks a bit like a swamp - but it's what hides underneath that intrigues divers, with people wanting to explore the cave system that in part runs more than 300 feet below the surface.
One video shared online offers a diver's point of view into the cave as they travel through a six-foot-wide passageway into the 'blackness' below.
The divers in the video explain that one of the caverns in the cave is 'about 400 feet wide', meaning you can't see from one end to the other.
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The roof of the cave prevents divers going directly back up to the surface if they run out of oxygen, meaning they're entirely reliant on their tanks.
"That's when a lot of accidents occur," one of the divers explains. "People don't have enough time to exit the cave [before they run out of oxygen]."
"In our training, we learn to use a third of our air supply to go in, a third for our way out, and a third for an emergency."
Another diver added: "There's a lot of people that have done this dive and not come home."
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The divers revealed that there's actually a warning sign installed in the cave for untrained divers, warning them not to go any further to 'help save lives'.
Among those who have lost their lives at Eagle's Nest include father and son Daren Spivey and Dillon Sanchez, who died in 2013, and best friends Chris Rittenmeyer and Patrick Peacock, who were found lifeless below the surface of the cave in 2016.
In 2019, Said Marjane died at Eagle's Nest after travelling to the site with a group to do free dives.
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When it comes to scuba diving, those taking part have to make sure they take breaks on their way up to the surface to make sure their lungs can adjust to the changing pressure.
"This is considered the Mount Everest of cave diving in a lot of regards," the divers explained. "Mount Everest is a very difficult place to reach on the surface of the planet, this is the equivalent underwater.
"We're very remote, we're very deep. This is a very hazardous environment."
Eagle’s Nest was closed to the public in 1999 due to repeated accidents there, but it was reopened in 2003 following a campaign.
Emily Brown