I'd love to have a few shots down there and get lost.
Very cool. It is interesting that the sides aren't brick or cinder block or something manmade, just carved rock. Is this typical?
Its blasted rock. They used explosives to create this tunnel. I think it has do with what type of earth they are tunneling through. Since this was solid rock I guess they didn't need to shore the sides or ceiling. Normally when its clay, dirt, sand, or something other then solid rock they use cement to shore up the tunnel and it would be dug instead of blasted.