Thousands of miles of tunnels and underground living passages have been found around the world, some dating back to 12,000 years.
Whilst some may be ancient mines many are just passages many with living spaces far underground, some have been built for thousands of people!
What would drive humans to make such effort? Were they just for protection from other clans and tribes as some do have obvious rolling stones to block access!
Research continues to try to answer these very puzzling questions!