I went "true spelunking" once. It gives me the willies to think back on it, even though it didn't bother me much at the time (young, dumb and full of .. uhm, bad ideas ). We did some "stovepipe" sections where you had to take your pack off and push it in front of you. They really weren't all that long before they would open up into a room but there is no way I would do that now. It was Case Cave in GA.