For centuries, mankind has wondered what lies hidden in thedepths of the Earth. For instance, what military secrets dounderground bases like Area 51 and the Cheyenne MountainComplex hold? And can discoveries in tunnels from the ancientpast--like the Tayos Caves of Peru and the Longyou Caves ofChina--illuminate the cultures of lost civilizations? Ashumanity develops and digs further into the Earth, includingthe search for rare elements, what else will we uncover?
