I didn't take this photo... it's from the web. Unfortunately, or fortunately, Kartchner Caverns does not allow photographs. They don't even let you bring your cell phone in!
We did two tours there: the one of the Rotunda Room, and one of the "Big Room" where they talked about the Cave's bat population. Both tours are worth it, although if you only have time for one, I'd recommend the Rotunda unless you are really into bats.
The formations were crazy cool, prolific and pristine. It's a living cave, and they've taken incredible steps to keep it preserved. They have massive doors throughout the cavern and only one door can be open at a time. They use a misting system to moisten the people in the tour so as not to change the environment within the cave in terms of humidity and such. Apparently, they even have "lint picking parties" where the staff goes in and uses tweezers to pick the lint off the walls, floors, railings, and even when necessary the formations.
We also did Carlsbad Caverns, which you'll see in another post. They are very different experiences, and I recommend both!