The first thing to say about Great Falls is that the best view is from the walkway on the Maryland side; the Virginia side is straight off the car park and has good disability access. But the Maryland side (just west of Potomac Village) is more atmospheric. You can walk down the C&O Canal, surveyed by George Washington in 18th century, past two locks, to a wooden walkway and series of bridges which take you right out to the edge of the Potomac as it falls over 150 feet to delta level. It is particularly stunning after a heavy rain, as the Potomac picks up water from Maryland and Pennsylvania. At my recent visit after Hurricane Sandy, the water levels were the hightest I'd ever seen and had completely swept over the island in the middle of the river. Even two days later, the footbridges were thrumming with the current.