Plot synopsis: Rob Bell climbs, crawls, dives and burrows into the amazing world of Underground Britain – in search of our most extraordinary, mysterious and challenging subterranean places, from hidden man-made constructions to stunning natural wonders. This is a journey into the unknown, discovering the other side of the story of Britain as Rob travels from the Highlands to Cornwall to uncover everything from modern engineering challenges to bloody medieval mysteries and weird ancient burials. Each of the six programmes focuses on a different region of Britain, exploring the best and most intriguing underground sites of Scotland, Wales, London, Northern, Central and Southern England.