I took it literally, as in subterranean vaults, stalagmites/stalactites, translucent and eyeless bodies, bioluminescence, underground rivers, etc.
"All I have is a piece of hard rock candy. But it's not for eatin'. It's just for lookin' through."
And as I posted this I realised you probably wouldn't be alone
And some "proper size" ones of CAVES - if you've not heard them, this is the DEAD MOON of now =) Awesome band!