Steve Backshall continues his search for wildlife in the jungles of Borneo. This time, his quest for the unexplored parts of the rainforest take him down a 160m drop, deep into a sinkhole. Getting in there and dangling on the end of a rope pushes his bravery to the limit. Once down, the expedition venture underground into a cave never before explored by humans, which turns out to be the stuff of nightmares.