Adam Spillane is just back from an experience that's out of this world.

Well... maybe UNDER this world is more accurate.

Spillane is a member of a British-Vietnamese Caving Expedition that's just returned from exploring a very impressive cave.

Adam...you entered what must be a caver's dream and you have photographs to prove it. What's the name of the cave?

Called Hang Son Doong in Phong Nha-Ke Bang National Park. The answer to our Geo Quiz.