Wow! Go to lunch and look what happens!
Rock Creek Park runs from the Potomac River near the Watergate Complex in a meandering fashion northward through NW DC and into Maryland. It forms the eastern boundary of Georgetown as it heads northward. The Rock Creek Parkway runs through the park, meandering along the creek itself, and is used as a major arterial for rush hour traffic. Rock Creek Pkwy ends at Connecticut Ave, NW south of the National Zoo. From there Beach Dr. runs past the back side of the National Zoo, as it meanders through the park northward into Maryland.
Rock Creek Park is a vast area, and I was honestly surprised when police searched the area so quickly. There are jogging/cycling trails that follow Rock Creek Pkwy, Beach Dr. and all of other roads in the park. Bordering the park are a large number of large homes and a number of apartment complexes. In addition, there are picnic and field areas scattered throughout the park as well.
In DC, the park is administered by the National Park Service; once you cross into Maryland, it is run by Montgomery County. I've got pretty good experience with the park; I used to live off of one of the side parkways when I first moved to DC in 83, and ultimately lived in an apartment complex just four or five blocks off the park once I got married in 85.