Pennsylvania Avenue/Seward Square Metro station (or, Penn. Ave/Seward Sq. Metro) is a fallen-in metro station. It can, however, be used by the player to quickly go between Pennsylvania Avenue and Seward Square.
Like just about any other metro station in Fallout 3, the outside of the metro is a few escalators going up/down to/from the doors to the metro. The outside of the metro is rather pristine compared to the inside.
The inside of the metro is significantly damaged and almost completely caved in. The Lone Wanderer can use the doors (and the holes in the walls) to pass from "section" to "section", but there is really only one way through. Inside, the player character passes through an office at first, and then what seems to be a waiting area or an engineer's locker room, as well as a couple of bathrooms. There are a few lockers spread throughout that hold some ammunition and supplies. The desks that you run into at first also contain some ammunition.