I remember several FTers posting on a TravelBuzz thread from a couple of years ago that it is possible to walk from Crystal City to DCA via the Mount Vernon Trail, and that there's both a "south" and "north" way to enter the airport on foot.

If the weather isn't too cold or icy, I'd like to try to walk to DCA on an upcoming trip just for kicks. I'll be flying Midwest, which leaves out of the old terminal (A). Where in Crystal City do I pick up the trail or street that leads to the airport?

Thanks!