Congested? Yeah, the Carlsbad Caverns are pretty cool. I've also been to several other systems around South Dakota. The Wind Cave is pretty cool. I much prefer dead (or wind) caves. Cold, not hot, humid, hard to breathe like living caves.
Yeah, there were so many people that it was shoulder to shoulder at times. *_*
I've only ever been in living caves, but Sonora Caverns is by far the hottest I've ever been in. Funnily enough, it was snowing outside so everybody was in their sweaters, and our guide (sadly there was no self-guided tour) forgot his keys to get us out the door at the exit, so about 20 of us are waiting down at the exit in sweltering heat for about an hour until somebody g=could get down to us. xD