Cycling through an abandoned tunnel in total darkness

Today I cycled through this tunnel. Somewhat isolated in the middle of the forest near the France/Luxembourg border.

I had heard that it is cyclable, but still I felt quite uneasy before entering it. It was a very weird experience. Quite scary, to be honest. The several small entrances on the side gave me some goosebumps.

The tunnel's length is around 500m.