Southern trail head (not well marked) in DC off of Park Road (just south of Piney Branch Pkwy) in Mt. Pleasant Neighborhood. Don't mistake trail for the driveway to the farmhouse estate just to it's south - it is a sheer uphill from the road. Northern Trailhead off parking lot of Beach Drive at DC/MD line.
Windy natural trail running through Rock Creek Park on the east side of Rock Creek. Southernmost two miles are mildly technical, but comes more smooth single-track for the northernmost 3 miles. One of the best inner-city running trails in the world.