The following video is already some weeks old, but I did not find the time to upload it. It is a little boring, especially after the readjustment of the headlight. Still, I hope it explains why I was a little afraid riding through the tunnel. Actually, there is a sign that one should walk the bike through the tunnel. This was on Stage 37 (scroll down).
Update: Auf Youtube gibt es noch mehr Videos, z.B.: .