For those that like to run, find solid places can be difficult in DC. Some are satisfied with jogging on the treadmill at the gym beneath Calvert-Woodley or at a local gym. However, both of these are too boring for many runners, myself included. Therefore, in the past summers that I have lived in DC, I've set out to find several greats spots and areas to go running.
The first is the Mount Vernon trail. The path actually begins in Roslyn, Virginia (a section of Arlington County) that is right across the Potomac from Georgetown and easily accessed by the Key Bridge. The 17-mile trail runs from the beginning of Roslyn through the backwoods of Arlington and Alexandria. The trail is mobbed with bikers and runners during the rush hour, as many take it to work in the DC area. But, at other times, especially as you get closer to Mount Vernon. Most joggers don't do the 17-mile trail in it's entirety (even though it is arguably best towards the end) but it is definitely worth the experience, if only for a couple of brief miles.
The second is the Monument Loop. This is best done in the early morning hours when traffic is light. Take the Metro to Farragut North. Run from the Metro Station to the White House for a brief Warm Up. There are then several possible routes to take.
However, perhaps most picturesque is as follows: run along Penn. Ave. to the Capitol, loop up behind the Supreme Court, and pass the Library of Congress and the House side of Congress before returning along Independence Avenue. You can then make your own route past the Washington Monument and back up to the White House.
With this, you successfully incorporate almost every D.C. landmark into a fantastic DC morning run.
Enjoy, and be safe!