Back in 2007, we visited an interesting park called Ringing Rocks County Park in PA. What makes this park so interesting is the large boulder field found in the middle of the forest. How did they get here, in this specific location? But it gets more weird! If you tap on any of the rocks within the field, they "ring". Many have been studied and cut open by scientist (and by jerky people) and found that what they expected (a hollow rock) was actually solid. It is just an interesting place.
Also while visiting we took the short hike down to the waterfall. Certainly worth the walk.