Our first adventure was the Historic Tour of Mammoth Cave in Kentucky. It was a really neat tour, covering 2 miles of tunnels in the cave. I recommend it if you are ok with that amount of walking! It was pretty narrow, short and steep in places, but that made for more cave-excitement.
Our tour guide was really personable and funny and talked about different aspects of the cave formations and the history of the cave and the area as we went through. The area was beautiful and green. The air was VERY humid and then became chill as we approached the mouth of the cave. We were surprised at how cold it was, even though we read about the temperatures on the website! I had intended to bring sweatshirts for the boys and then had forgotten, but they kept themselves warm enough by being their usual "energetic" (ahem) selves.
We tried to take pictures but it was really difficult to get good shots (here are some if you want to see more) in the darkness of the cave. The pathway was lit, but dimly. There were some very large rooms plus areas we had to scoot sideways through or duck down for quite some length. At one point they turned off all the lights to show the darkness of the cave, then lit just a kerosene lantern to show what early explorers would have had to see by. We crossed The Bottomless Pit and heard about how the first explorer of the area crossed on a beam he rested across it, rather than on the steel bridge we had!
The boys really enjoyed it, though it was a little long for Sammy who said it was "too many walking". But really, it was fine for him until the very end. If you have the chance, give it half a day or more.
If you do, one last note - we went to the first tour of the day, buying our tickets online ahead of time to be sure we could go at the time that worked for our schedule. We were glad we did because the tour sold out, but that was also the downside: it was a HUGE group. The next tour was much smaller. We would have preferred a smaller tour because the group had to rush in many places to make up for the backup that would form in the narrow/steep places. I think a smaller tour would have let us go at a more even pace and see more.