I'm going to guess it was the C&O canal and Berkeley Springs. The C&O Canal ran from Georgetown (Washington DC, now) to cumberland Md. along the Potomac River, and stopped at or near Berkeley Springs, WV.I am assuming the canal that runs through Georgetown is a remnant of the C&O Canal. The C&O railroad also ran a similiar route, and the Railroad and the canal may have shared PawPaw Tunnel, which is also near Berkeley Springs.
Google the C&O Canal and Berkeley Springs--also Harpers Ferry--to find more information.