Over 120 thousand years ago the Arabian desert was a pathway for the first human migrations out of Africa. On this expedition, Steve and the team start their journey at the ancient Nabataean city of Hegra, where secrets lie waiting to be uncovered.Joining forces with Saudi Arabian geologists Mahmoud AlShanti and Hala Alwagdani, Steve and ropes expert Aldo Kane head down into an unexplored?volcanic underworld in search of the longest lava tube in Arabia. Geological evidence suggests that at least 400km of tunnels lie beneath the rocky lava fields?above –?subterranean passageways which could contain the bones and artefacts from ancient civilisations. Only 25km of these lava tubes have ever been unexplored… until now.