I am new to DC Tri and I am looking for good paths that are metro accessible. I live in Georgetown so I already know of the bike path in that area (C&O, Mt. Vernon, etc). I'm looking for somewhere more out of the city.
Getting from the Vienna, VA metro to the W&OD Trail, which can take you out to the foothills of the Blue Ridge, is pretty easy through back streets:
Bikes aren't allowed during commuter hours tho.