Although I loved the historic old town too, my favorite thing to do in Harper's Family was walk along the canal trail.
I started from the main visitor's center, and walked the trail (fairly steep, with some steps) down to the armory canal trail. Like the name implies, it goes along the old canal. The canal is now mostly marshy, and teems with wildlife: I saw a blue heron, huge fish (carp, I think), and the biggest turtles I've ever seen in the wild.
The trail also goes by an old factory, and several other ruins. Plus there's a bridge you can walk over. The canal area really has a gothic, romantic feel to it. It reminded me of something you'd see down south.
Best of all, most visitors seem to stick to the main town, so many times I had the trail to myself. The farther you walk from the town, the marshier/less crowded the trail gets.
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