By Anna Edwards in Mail Online
It's an adventure that demands explorers spend their time in the cold, wet and dark.But for those who persevere, the results are certainly worth it.
A French-Swiss team have made it their mission to explore a huge network of chambers and sinkholes beneath the Nakanai Mountains of New Britain, in Papua New Guinea.
And for those who thought it was just the lush mountains and forest of the country that were beautiful, think again.
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| A caver stands in a chamber of stalagmites in New Britain, Papua New Guinea |
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| Deeper underground: A man stands in a white chamber observing the stalagmites in the yawning cave |
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| A team of cavers step through the water in a cave as they explore the networks beneath the forest |
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| Is anybody there? The team are on a mission to explore the miles of chambers and sinkholes |
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| Don't look down: A caver abseils above a pool of water in a cave, watched by French photographer Philip Bence, who described it as an 'incredible and unforgettable adventure' |
'The desire to explore remains the reason why cavers cave,' said Mr Bence.
'It is a privilege to have the opportunity to discover virgin terrain, to be the first to explore an area, to draw the map, to name a cave and its features.'
They abseiled sheer faces and dived through underwater chambers to reach new sections almost 600m from the upper entrance.
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One caver prepares for the next part of the expedition - plunging into col water, as the team delve deeper into the underworld  |
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| Into the wild: A caver stands in a dark cave s they descend into the unexplored darkness |
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| Head for heights: The team begin their long descent into the caves which stretch for miles in the beautiful country |
The main danger for 13-strong team was flooding - due to the unpredictable and heavy rainfall in the tropical island - and they had several close calls.
Cavers first entered the site in 1980 after hearing about huge openings in the middle of the tropical forests.
Mr Bence, who took part in five expeditions into the caves, added: 'Each generation of cavers has continued to reveal this hidden world.
'The subterranean environment is a fantastic place for discovery, for adventure and we are certainly lucky to be able to enjoy exploring it.'
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| Using ropes, a man abseils down a white chamber in the cave network, as the team discovers the extent of the underground network |
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| Peekaboo: This tiny mammal with its huge curious eyes is capture on camera in the pitch black cave |
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| Waving goodbye to daylight: A caver prepares to drop into the cave network which remains largely unexplored |