One of our little informal training exercises with the Oregon Grotto was to climb in a select lava tube cave a couple miles, then kill the lights and try to find our way out. It is almost impossible not to lose your nerve and start flinching after bumping your head a dozen times. Such a complete absence of light does enhance your hearing, in unsettling ways until you get used to it. Climbing over the breakdown was a real pain.

It was a good exercise. But not for the faint hearted. 2 miles underground in the dark took the better part of 6 hours, and that in a cave we were already familiar with. In big chambers, it is dangerously easy to get completely turned around, and start back down the way you came.