A seventeen mile ride through closed streets in the nation's capital. I had a great time when I did this in 2016. Riding the national mall and past the pentagon without any cars to contend with was memorable to say the least. Only downer was a light rain for the duration of the ride. Learn more at DC Bike Ride.
I stayed in Bethesda and was able to ride the Capital Crescent Trail to the start of the ride. After the ride I met my wife and was able to bring my bike on the subway that stopped under our hotel.