Nada Tunnel is just cool! There is no concrete, steel, or anything at all reinforcing it. It's just jagged rock inside! It's only a narrow one-lane tunnel, so you just swerve your vehicle out into the middle of the road and see if anyone is coming before you go. The Red River Gorge Geological Area of the Daniel Boone National Forest in Eastern Kentucky begins as you emerge from the other side of the tunnel.