Our side trip while camping this year was to Harpers Ferry, a historic town in West Virginia that sits where the Potomac and Shenandoah rivers meet. It's about an hour and a half from Baltimore, so manageable in a day if you aren't up for the overnight. Most of Harpers Ferry is either national parkland, or historic district. The Appalachian Trail also crosses through. So beyond the amazing views, you will find lots of hiking, tubing, and history here.
Parking is a challenge, unless you arrive early, but a shuttle runs every 12 minutes from the Harpers Ferry National Park to the historic district.
There are museums and shops along the way.
Be sure to climb up to visit St. Peter's Roman Catholic Church. The church is beautiful and open to the public. And the view from way up there is not to be missed.
There are a shocking number of icecream shops around. Really, Harpers Ferry? I think you may have over-saturated yourself with icecream shops. We eventually gave in.