one line from House of Leaves in particular sticks with me, a quote from a (fictional) french caver:
“Darkness is impossible to remember. Consequently cavers desire to return to those unseen depths where they have just been. It is an addiction. No one is ever satisfied. Darkness never satisfies. Especially if it takes something away which it almost always invariably does.”
I used to be into caving. There's something transcendental about complete darkness. Not just the merely dark of an overcast, moonless night, but the truly black. Caves are the only place I've seen it. No visible-wavelength photons beyond those made by radioactive decay, maybe.
It's uncanny. Humans aren't built for it.
Most people begin to gently hallucinate after anywhere from a couple minutes to a half hour.
A friend of mine would get scary, non-gentle hallucinations. She didn't like the lights to be out for longer than a few seconds.
I miss that kind of darkness.