Circle trip from DC to Front Royal, VA, then on to Hagerstown, MD, and then into Harrisburg, PA. Exiting AMTRAK's Keystone line at Royalton, PA, the special train heads back to DC on the freight-only Port Road to Perryville, MD and then onto AMTRAK's Northeast Corridor line back to DC.
Details and ticketing are here:
http://www.railsnw.c...g/Main_Page.htm