Starting from the east going to the northwest, the layout of the entire district is blocked paths of rubble from collapsed buildings, destroyed streets, rocky pathways, and finally super mutants infesting the area. Immediately to the left is a Metro station called Pennsylvania Ave/Seward Sq. Metro, and continuing forward will lead you towards a large rubble blockage which has a route going to the right, where you will encounter three to four super mutants depending on your level; who will either be normal, brutes or even super mutant masters. To the left of the diner and behind the large rubble to the right will be an entrance to the sewers and if you proceed farther down the road, you will discover the Northern part of Pennsylvania Avenue; where you will find the Freedom Street station and possibly a dead Wastelander. Traveling directly south of the station will lead you quickly to the southern part of the avenue, where you will find the Penn. Ave/The Mall Metro tunnels, to the left of a destroyed car and rubble and along with being surrounded by a partially destroyed building. Once here, turn around and take a left to continue through the district where you will encounter a group of super mutants fighting with the Brotherhood of Steel on the other side of the street, where they are bunkered down. Passing the Brotherhood troops will lead you to a statue which appears to have 4 golden women each holding a large bowl. Behind them is a man-made fence blockade. To the left of the statue is a large hotel which the Brotherhood use as a base of operations, and to the side of the entrance to the hotel is the metro tunnel called Penn. Ave/Georgetown Metro.
At the scaffolding at corner of 17th and Pennsylvania, there is a dead merc on the side with the leaning/bent light pole (you must walk up the pole to reach the merc) with a note (Pennsylvania Ave explosives note) about planted mines and activation switch location. The switch is past the dead merc. When you activate the switch, all the explosives go off in a chain reaction in the street.
Next to the Metro Central is an old trailer-style diner. In it are several gore bags and five ammunition boxes (to your left as you enter), with some 5mm rounds, 10mm rounds, a missile and a grenade box with frag grenades in it. There are also several mutilated wastelanders, wearing enough leather armor to make a fully-repaired suit.
Down the utility tunnel, to the right, is a great place to make custom weapons, with parts and a workbench located nearby.
A destroyed building (The White House) accessible via the underground utility tunnel containing some RadAway, a Fat Man, and three mini nukes.
The streets in this neighborhood appear to have been misnumbered in the game, as 17th Street is west of the White House. The street marked as 17th Street in the game should probably be 12th Street.
The White House Plaza is already in the main game but is not marked on your Pip-Boy until you have installed Broken Steel.
Getting to any of the loot mentioned above can be difficult depending on the path taken towards it.
The White House Plaza can be found near Pennsylvania Avenue, while the path to get there involves backtracking and going through an irradiated section near the actual Plaza, but as stated above Broken Steel needs to be installed to see the exact location on your Pip-Boy.