Loads of us have GoPros these days to capture incredible moments while we're out and about adventuring - but sometimes, they record footage of things we'd rather not relive.
Out of the five Finnish men who descended to the depths on 6 February, 2014, only three of them made it back up - and a GoPro chillingly filmed the moment things went fatally wrong.
Patrik Gronqvist, Jari Huotarinen, Vesa Rantanen, Jari Uusimaki and Kai Kankanen had made the risky dip into the idyllic pond Plura, swam underground for half a kilometre and emerged into a long, colourful cave.
Most people brave enough to complete the expedition hop out of the water, admire the grotto and then resurface - but experienced divers often carry on further to find a icy cold area of water in complete darkness, known as a 'sump'.
If you make it through, you will eventually ascend to the cave of Steinugleflaget and you can then exit via a crack in the side of a collapsed hill - which already sets the health and safety alarm bells ringing.
"The deeper part is very demanding, very cold water and narrow tunnels, and deep as well - it is the world's deepest sump that has been dived through," Gronqvist told the BBC.
It's a gruelling five-hour trip which challenges you to dive to depths of more than 130m with only underwater scooters to help you move faster - but the five Finnish divers reckoned they could handle it.
At some point, Gronqvist realised his good friend Huotarinen was no longer behind him - so he went back to find him only to discover he had become trapped in a narrow part of the cave and entangled in a cord connected to a piece of his equipment.
He tried to help his panicking pal by giving him a cylinder of gas to reduce the amount of carbon dioxide in his system, but the diver began to swallow water while changing breathing apparatus - and died in front of him.
After desperately trying to free his body, Gronqvist had no choice but to continue for his own sake.
Rantanen was the next diver to pass through the narrow area and past Huotarinen's body - leaving him to 'decide what to do' in just a matter of seconds.
He said: "My options were to try to pass that dead diver, or to turn around and try to do a very long dive back, go back to the deepest section and try to survive to the surface. I decided to go forward, and that was a very good decision for me. "But it took me at least 15 minutes to get past that dead diver."
Unbeknownst to him, Uusimaki was following close behind and had also ran into difficulty.
Norwegian police believe he panicked after seeing what had happened to Huotarinen and drowned - and despite the fifth and final diver, Kankanen, trying to help him, Uusimaki tragically also died during the descent.
Kankanen decided to ditch his plans of reaching Steinugleflaget and turned around to return to the surface - which saw him finally emerge from the water in the early hours of the next day, after having to smash through a thin layer of ice.
It was more than 11 hours after the group had set off on the dive which was supposed to take five hours.
After eventually making it back to the surface, the three survivors - Gronqvist, Rantanen and Kankanen - were all hospitalised with decompression sickness and authorities closed the cave and were reluctant to try and retrieve the bodies, as it was deemed to be too dangerous after a team of British divers were unsuccessful.
A diving ban was brought in for the cave - but the Finnish divers took it upon themselves to launch an off-the-books repatriation mission, despite still suffering from decompression sickness and other injuries.
Without official authorisation, the trio and other experienced divers later returned to retrieve their friends bodies.
Gronqvist told the BBC: "I told the widow [Huotarinen's wife] that we would go and get them. I told her that they are not going to be left there, that we would think of something."
The recovery expedition was filmed as part of a documentary titled Diving into the Unknown, which showed how the bodies of Huotarinen and Uusimaki were successfully brought to the surface following the five-day operation.Featured Image Credit: YouTube/MrDeified