Rarely mentioned National Parks and Monuments.

I don't see it mentioned much here but Big South Fork in TN/KY is one our favorites. https://www.nps.gov/biso/index.htm A couple of nice developed campgrounds and also more rustic camping. Some interesting trails and dirt roads to explore. There is a well interpreted historic mining town as well as the "utopian" town of Rugby. The campgrounds are popular with horse people but they have their own trail system and the horses are kept well away from the campground.