I was truly surprised at the length of the tour (we took the one that is about 1.5 hrs) and how large the caverns are. The ranger was very knowledgeable. This is the second longest cave in the world (Mammoth in Kentucky is the longest) and the tour, while long, only goes in a small part of it--I think as of August 2011, there were 150+ miles of mapped cave tunnels. You should try to book up to a week ahead, especially if you are going in the summer peak season. We went after Labor Day, but the tour was still pretty full. Warning: you will probably have to call several times--due the volume of calls, you sometimes only get a recording. Some other reviewers complained about rangers who yelled at them for not coming exactly 30 minutes before the start of the tour--I did not hear anything like this the day we were there. We were about 20 minutes early, instead of 30 minutes, (delayed due to road construction) but no one said anything to us. Warning: there are lots of steps on this longer tour. I highly recommend this attraction. It was really impressive.
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