During our last visit to the Black Hills I wanted to show my wife one of the caves. We stopped at Wind Cave and found there was an hour and a half wait for the next cave tour and it was one that lasted two hours. We didn't want to invest 3 and a half hours so we drove on. After spending the night in Custer we then tried Jewel Cave (another National Monument) early the next morning only to find we had to make a reservation for the afternoon so we left again. Later that day we stopped at Rushmore Cave near Keystone. This is a privately owned cave but still under strict federal control. We waited 15 minutes for an hour long tour led by an enthusiastic young guide and had a wonderful time. There's a nice gift shop and also a zip line that's a lot of fun. Most of the crowd had children with them who seemed to also be enjoying themselves. I'd recommend it to anyone.