One of the most famous caves in the US is the Mark Twain Cave in Hannibal, Missouri. It was originally discovered in 1819.
One thing about this cave is that it served as a hideout for the notorious bank robber Jesse James, so it definitely has an interesting history.
But another interesting aspect is that this cave’s maze of passages inspired Mark Twain to write about Tom Sawyer and Becky Thatcher getting lost in McDougal’s Cave. (Great book BTW!)
Who says caves / tunnels / secret passages / mazes aren't inspiring? Plus they're fun!