I went on a tour of a mine today. I actually wasn't claustrophobic! The guide turned off the lamp to show us what absolute darkness was like. Hmmm...how can I describe it? Well, imagine yourself in a cool, breezy tunnel in the rock with the entrance about 30 yards down several turns in the path, with no light at all. No light from lanterns, flashlights, headlamps, phones, or other devices. Just a heavy wall of blackness. Even when you blink, you can't tell the difference. That, my friends, is absolute darkness.
It was awesome!!!! Now I have a good experience to draw ideas from for my story.