The largest natural tunnel

This huge natural tunnel is located on river Glada (golden, in north germanic languages), between the capital and the end of the Chasm-Canyon gorge.

As I have described in the post about the Emerald Valley, when the Glada Lake emptied catastrophically, its waters bored their way down the new path for a long time, long enough to form holes in the landscape, natural arched gateways to the Valley, and this natural tunnel. As you can see the opening is an irregular oval, in the foreground the tunnel is more round, and then becoming a flattened oval. The tunnel is about 200 feet long and 50 to 140 feet high in places.

Natural hot water waterfalls issue from many locations on the tunnel walls, and the largest spring has been harnessed into the pipes and ducted into the nearby geothermal power station.

The hole in the ceiling has been drilled in the early 1930's.