A long time ago, a seasoned roady told me he went through a fairly long tunnel on the N.C. parkway, one that is curved such that at the ~midway~ point it was so dark he couldn't make out light at either end. He said it was the most scared he's ever been. (I assume he rode it at speed).
Before he took up riding, he was one of the boldest rock climbers around, among the first to solo whitesides mtn. in the 70s. It's ~1000' high so I imagine he had a good grasp of managing fear.