The Chesapeake and Ohio Canal, usually referred to as the C&O Canal runs parallel to the Potomac River from Cumberland, Maryland to Washington D.C. A length of around 184 miles. It operated for almost 100 years (from 1831 to 1924). It is now maintained as a National Historical park and makes an excellent walking/running/cycling route.
This photo was taken opposite Harpers Ferry. The fog from my other photos is still clinging to the hillside here.