Even though Washington DC is the Capital City it has a wealth of running trails and green spaces.
The National Mall is an easy 4 mile loop route from Capital hill to the Lincoln Memorial. It is said to be one of the most run routes in the world. It passes various museums, memorials and monuments. It is a flat route made up of gravel or side walk. The route can easily be extended to include The White House and other points of interest. You can also pick up the Cherry Blossom Official 10 mile run in this area. This run is officially around the start of April with fantastic views of the Cherry Blossoms. Best to get to this area early or late as it can get very busy with tourists during the day time.
Rock Creek Park is another favourite – it has various popular trails offering a variety of different terrain. The Southern section has some nice wooded sections which run past a creek and the Zoo. The North section is partly on Beach Drive so can be a bit busy with traffic. Western Ridge Trail is a popular 5 mile dirt trail- although it is dirt the terrain is quite easy to handle for all abilities and trakes you past some nice views of the river and woods. Valley Trail is slightly more challenging – it has a lot of up and down and you need a bit more care not to lose your footing on rocks and roots. It was a little more like a scrambling hike in some sections but it was still a lot of fun and it broke the run up.
The Chesapeake and Ohio Canal Trail is 184.5 mile long! Perhaps better suited to on a bike than on foot but sections of course are nice for running- it is pretty flat and as you would expect from the name it runs along the Paromac river and has lovely views.
Washington DC is not only has a number of nice runs it has a nice running climate and a lot of marathons and fun runs. See what might be on on your next trip.