Gettysburg is only 45 miles NW of Baltimore, Valley Forge is about 85 miles ENE. Don't know what schedule is at the Daniel Boone Homestead, about 60 miles NE of Baltimore. Dixon's Muzzle loader shop is about 85 miles NE of Baltimore. Ft. Frederick's 18th century Market Fair is the end of April about 50 miles NW of Baltimore (a big encampment at a real F&I era fort. Harper's Ferry about 70 miles WNW of Baltimore. Sky line Drive, about 80 west of Baltimore. Ft Shanandoah outside Winchester VA, has the NSSA National Spring skirmish in early May. About 60 miles north of Baltimore is wrightsville, PA, where the feds burned the bridge to Lancaster to stop the advance of the Rebs.
The area is chock full of historical stuff, far to much to list all of them. In fact, there are so many historical sites, that folks make a joke out of it. A friend out side DC, has a brass plaque mounted in the hall way at his office that reads something like "On this site, on August 23, 1885, absolutely nothing of historical significance happened."