Honestly, they’re pretty neat. I’ve gone through tours of Mammoth Caves that require waivers, and they strongly recommend that you not take that tour if any part of you has a circumference of more than 42", because you won’t fit. There was a spot that was about 12" high, and 72-ish wide that you had to crawl through that took a sharp right; you had to take your helmet off to get through. But then you get out into this enormous cavern filled with rock formations that are seen by less 100 people/year.
But if I didn’t know that that crack was passable, that I’d be able to get through or get back out again? Fuuuuuuuuuuuuuuuck no.