I've seen a few on here that are rather good. I personally am very tempted to make my own, as a catacomb is very fantasy, and a metro is very post apocalypse, but a cave, well that is universal!!
Did blueVT do one? If you search In the workbench or fantasy forum some come up.

and I remember seeing some outstanding ones! Caverncrawl/trapdoor is a ruleset which was played on an awesome looking board.
I'm pondering mdf rectangles as bases, and cork/bark walls. Making it with modular windy corridors and larger 'halls'. Possibly doing half height walls to save on space without loosing too much aesthetic.
Cheers
Matt.