Even here in the 21st Century, we are still finding lost or forgotten worlds. It’s amazing that these giant cave systems have survived countless ages of geologic activity. Funny, though, how many lack any significant remains of human activity. On the other hand, there are legends like those in South America that claim there are many hundreds of miles of subterranean tunnels once used by the Incas to hide from their enemies and stockpile gold.
And on 
Darrick Dean 