The climbers are pictured lowering themselves downward into the 350ft 'Rumble Room' - a limestone cavern in Tennessee thought to be one of the biggest caves in the U.S.
The intrepid cavers reached the cave by plunging down large waterfalls, shimmying through tight underground spaces and swimming in the world's most remote underground rivers.
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| Spectacular: Lit up by the glow from their torches these cavers look like tiny toy soldiers as they admire the spectacular rings of rock at the bottom of the Rumble Room caves in southern Tennessee |
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| Daring: With water shooting past as they go, the explorers carefully descend a stunning rock face as they explore the 2,000ft of passageways |
Their reward for the daring downward climb is exploring the gaping Rumble Room chamber, a mammoth cave surrounded by around 15 miles of river passages and waterfalls.
Cavers and ecologists look to have preserved the future of the spectacular cave, after plans had been revealed to allow up to 250,000 gallons of sewage through it.
But opposition from the Conservation Action Network defeated the sewage treatment plans for the nearby town of Spencer, Tennessee, and the enormous cavern has remained uncontaminated.
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| Plunge: The descent seems to go on for ever as the cavers make their way towards the entrance to the Rumble Room |