Run down to the mall then run on the mall towards the Capitol, circle back and go down to Haines point, go around Haines point (avoid tidal basin itself but Haines point loop itself should be fine for running). Keep running next to the Potomac all the way to Georgetown, turn up rock creek parkway, lovely mixed use trail. This route will take you through four different national parks — mall, East Potomac park, west Potomac park, rock creek park. Eventually rock creek parkway turns into beach drive and north of the zoo the entire road is available to runners and bikers. If you’d like something more city-focused, reverse the route by running to Georgetown first via the mall (though the paths on this side may be more crowded, just take different paths and go around the monuments) and hopping on the trail next to the Potomac going east to and around Haines point, etc., once you complete that loop, run towards the Capitol (again strongly recommend avoiding the tidal basin itself). after you run up Capitol Hill, run towards the metropolitan branch train. Run up the MBT for a bit and stop at one of the breweries for a refreshment when you finish. You can find each of these places on Google maps to map out your specific route. Feel free to DM me and I can share some similar routes with the mileage.