Ohio and Erie Canal Towpath Trail

The Chesapeake & Ohio Canal National Historical Park (a.k.a. C&O Canal Towpath) follows the route of the Potomac River for 184.5 miles between Georgetown in Washington, D.C., and Cumberland, Maryland. Hundreds of original features, including locks, lock houses, aqueducts and other canal structures, are reminders of the canal's role as a transportation system during the Canal Era, which peaked in the mid-19th century.

http://www.traillink.com/trail/chesapeake--ohio-canal-national-historical-park.aspx