In 2007, a team of 41 cavers worked their way into the limestone of the Arabika Massif in the Western Caucasus, Georgia, to descend to new depths of the Voronja Krubera cave system. Two branches of this subterranean warren were discovered to reach 1,775 metres (5,823 feet) and 1,920 metres (6,299 feet), but the deepest point – a sump dubbed ‘Two Captains’ – exceeded the two-kilometer (1.2-mile) mark to become the deepest natural cave in the world at 2,191 metres (7,188 feet).
Essential kit used for casual spelunking (or potholing) includes a hard hat, headlamp, waterproofs, thermals, climbing gear and basic rations for longer expeditions. But the 2007 Krubera caving trip was comprised of professional spelunkers, known as speleologists, who weren’t just experienced at exploring caves but specialists in cave sciences including biology, hydrology and geology.
The 41 team members spent a total of 29 days mapping out the cave network, as well as recording the temperature and sampling sediments, micro-organisms and speleothems (which include cave formations such as stalagmites). So as well as standard camping gear, sample containers and more unusual scientific devices such as ground-penetrating radar were used to help plan the best possible route ahead.
Georgia (specifically the disputed region of Abkhazia) is home to the top three deepest caves on Earth and, incredibly, Two Captains is known to go deeper still. Ropes and carabiners in the hands of expert climbers are essential for exploring these incredible depths, as the Voronja-Krubera system includes drops like the Big Cascade, which alone plummets 152 metres (499 feet).