Lave Tube

While we are on the subject of Volcanos & such, There are some lava you can walk through... You need to bring your own flash light... but the fun part is when you get right into the very middle of them and turn off your light. Dark, yes, very dark. and very quiet, (especially if you manage to be there off-season... but you don't want to do that) It is so dark and quiet that you start hearing things creeping up behind you! Ooh! Thrills!

California
Lava
Tube
Tunnel
Underground