I'm not a huge fan of the trails out here. The W&OD is the granddaddy, of course. Fairfax County Parkway has a connector trail to that one. Fairfax Cross County trail is pretty entertaining in places if you have a mountain bike.
Living in Alexandria was more fun - I had the Mount Vernon trail, Four Mile Run trail (which eventually becomes the W&OD) Custis trail, then you could cross into DC on any of the bridges and bike all around the mall / tidal basin / Hains Point areas. Awesome people watching.
Stopped for a moment on the Memorial Bridge, looking down and saw substantial nudity in a boat crossing under the bridge
- definitely not allowable on the WNF
amilyF