Hidden beneath our feet lie extraordinary spaces, caves and tunnels. They’ve been designed and built by us as well formed by nature. But how were they created and adapted? By whom, and why? For centuries, subterranean structures have captured our imagination. Now we’re going further and deeper to unearth the stories, the mysteries and the secrets of Underground Worlds. This stunningly-shot, epic series reveals the hidden stories of some of the world’s most extraordinary underground structures – natural and manmade. They’re brought to life with beautiful visuals, personal and expert testimony, archive and graphics. Each episode features three complimentary underground worlds and unpacks each unique story – from its conception, its construction, its uses and, in many cases, its repurposing for different future uses. Every underground world is different and each has a fascinating story hidden deep beneath our feet – until now!