During my recent trip to DC, I stayed in the Ballston, Virgina area instead of my typical Crystal City stay.

My hotel ended up being right next to W&OD Trail system.  I had some great runs on Thursday and Friday morning (even though I got completely soaking wet on Friday morning).

Make sure you plan accordingly if you visit the DC/Virgina area especially if you are a runner or a biker. 

The Crystal City area also has some good access to similar trails. A great resource.