Here are the directions from Baltimore:
Take I-70 west towards Frederick. At Frederick, look for the U.S. Highway 340 exit. Take the "Harpers Ferry 340 exit" heading south (the exit sign may actually be shown as 340 west) towards West Virginia. After crossing over the Potomac River bridge make a left shortly afterwards at the traffic signal (VA Highway 671). Take VA 671 to the end where it meets up with VA Highway 9 (traffic signal there). Make a left at VA 9 heading east. Travel on VA 9 for a relative short distance and look for Cider Mill Road on the right. Make a right on Cider Mill Road. Follow Cider Mill Road to Woodbridge Road (another relative short distance). Make a right on Woodbridge Road (County Road 719). Take Woodbridge Road (less than about five miles) to Appalachian Trail Road (County Road 713). Make a right on Appalachian Trail Road. This road will take you to Blackburn.