I watched one of the episodes of Planet Earth the other day. The one about caves. I have tried caving once or twice. Not too happy with the possibility to die like a worm underground though.
But the Lechuguilla cave and the pictures from the chandelier ballroom was amazing! I can't get it of my mind.

I would certainly be ready to overcome some claustrophobia to see that with my own eyes one day. Doesn't seem to be a place for guided tours though... talk about going deep, about 500m down from the surface... Anyone want to come along?