I had the opportunity to re-visit Indian Caverns in Spruce Creek, Pennsylvania on the trip to Penn State.(http://www.indiancaverns.com/).
It's a neat little cave with good guides, affordable price, and accurate information about the Native Americans who frequented the cave, beginning at least 10,000 years ago
The cave is under private ownership and well maintained.
I recommend visiting the cave to understand some local prehistory and to see for yourself how limestone caves form and are continually evolving.
Well worth the trip. It's on a very scenic route and only about 1/2 hour from Penn State.
A few photos from Indian Caverns:
The entrance is on a hillside.
Here, one of the stalactites was unfortuantely broken off. One can see inside of it. It's hollow!
Cool stalactices!
See the green? Unfortunately, from all the humans trapsing inside the cave (including me), algae is growing on the walls. This problem was a major one for Lascaux, France where the government closed it to visitors and built Lascaux II. There are no cave paintings that have been found at Indian Caverns.