Watch this until the end and you will get a revealing insight into what these tunnels are now being used for. An ancient tunnel system may have spanned the entire Earth, from continent to continent. Seems hard to believe at first but there are many legends and tales of subterranean worlds scattered throughout old texts. There are also fascinating caves and cities that have been discovered under our feet, but no one seems to know who built them or for what purpose. Some people an advanced civilization built them in a time before recorded history. Could they be right?