Run the C&O Canal towpath along the Potomac, starting and finishing beside Lock 20 at Great Falls Tavern. All three distances head south along the canal past Widewater, Old Angler's Inn and Carderock, then turn for home. The towpath is flat, shaded crushed stone that was built for mules and is perfect for a fast fall race. Late November is the towpath's best season: the crowds are gone, the air is cool, and with the leaves down you get long views of the river.

Start times: Half marathon at 12:00 PM, 10K at 12:30 PM, 5K at 1:00 PM. Finish line closes at 3:00 PM.

Good to know: the field is capped under our National Park Service permit, so register early. The park charges $20 per vehicle (card only) at the Great Falls Tavern gate, and parking is limited, so carpool if you can. The towpath stays open to other walkers and cyclists: keep right and pass on the left.