Cavin'
Mammoth Cave in Kentucky is one of the oldest tourist sites in the country with 360 miles of underground caves identified. We took the 2 hour, 3/4 mile tour going 200 feet down, and of course back up!
We were in a group of about 40 people with several little kids who asked some interesting questions. I think it's actually harder on the knees to go down than up. Some places were so narrow you had to turn a bit sideways.
And then you come out into wide open spaces and feel you can breathe again. I was a little apprehensive about this. Would it be too strenuous? Would I get panicky being underground? Well, I/we did fine. For me, I just couldn't think about the fact that we were 20 stories underground!!!
At one point, at one of the brief sitting spots, Ranger Charlie had us turn off or cover up anything that was lit up, like camera lights or blinking shoes. Then he turned off the lights and....wow...absolute pitch black. Couldn't see my hand in front of my face. Then I thought about actually "spelunking" and I know I could not do that. It was a great experience and we decided that we'd like to see Carlsbad Caverns in New Mexico also.