Central Pennsylvania is home to many underground cavern tours. My family and I were recently on a trip to central PA and were staying in State College. The nearest underground cavern was Penn's Cave & Wildlife Park, it was bout 20 miles away. Plus it is the only all water underground cavern tour around. So we decided to give this one a try!
It is a one hour guided tour by motorboat. The price was just over $40 for the four of us - 2 adults and 2 children. We walked a long path down a hill and then down some steep steps and boarded the boat. The boat felt a little wobbly at first and I was a little unsure, but it was fine once everyone got loaded. There were about 20 people on our boat. Our tour guide then proceeded to drive the boat into the cavern. He stopped at several different places and told all kind of information. He was very informative and fun. We had a very nice time and the kids really enjoyed it.
I would recommend taking your family to see this natural wonder if you are ever in the area. Remember to bring a jacket, the cavern is a constant 52 degrees year round! There is also a 90 minute wildlife tour on this property given by bus, although we did not take that tour.