As Brown's raid deteriorated into failure, he and some of his men took refuge in the armory's small fire engine house, which would eventually become known as John Brown's Fort. It has been moved from its original location, but today sits next to the intersection of Potomac and Shenandoah Streets.
On the other side of John Brown's Fort was a historical exhibition.
The Maryland side of the Potomac can be reached by a walkway attached to this railroad bridge. The walkway is part of the Appalachian Trail, which runs through Harper's Ferry.
On the Maryland side is the Chesapeake and Ohio Canal towpath, which extends from Washington, DC to Cumberland, Maryland. The canal (or more precisely, what's left of it) and towpath form a National Historic Park. Near the Maryland end of the above bridge is the remains of one of the locks.
Here's part of Harper's Ferry as seen from the Maryland side.