Beneath Borneo’s rainforest lies one of the worlds largest cave networks. So far 300 km of passages have been discovered; with more being found on every expedition. Monty and Leo are on a journey to explore this subterranean Lost World. Their first destination is a 50m deep sinkhole – a collapsed part of the cave system. It was first discovered in the early 80’s and Monty and Leo may be the first to venture there since. Monty plans to carry out a wildlife survey, likely to be the first ever, while Leo will search for a passage connecting the sinkhole to the rest of the cave network. Phase two of the expedition is to explore a nearby cave. Since cavers last explored this area over 30 years ago cave lights have improved ten fold. It is very possible that Leo and Monty can find new passages that were missed on the first survey.