In L'Enfant South, there's an office building that once housed the Capitol Post newspaper (simply marked "Office" on the local map). The building contains a few computers with the text of the articles that appear on the loading screens. In the basement of this building you will find Gibson's corpse with a key and a note saying "Search the house!". The house is the Gibson house located in Minefield, and the key opens the model of home on the ground floor of the Gibson home.
To the west of the Capitol Post newspaper office is the L'Enfant Café (C). The cafe has a few dead raiders, two first aid boxes, some Buffout, and a mine box.
The Lone Wanderer may encounter a vertibird landing on the central crossroads, which usually results in a major firefight between the Enclave soldiers and super mutants in the area. With the addition of some exploding vehicles, this is likely to result in many dead enemies with minimal effort.
Just as the Vertibird lands, if you shoot at the nearby tractor trailer truck it will create a chain reaction (with other cars in area) of nuclear blasts that will take out all mutants and Enclave soldiers. A final shot with a missile or grenade will take out the damaged Vertibird, or simply shoot it with the Tesla cannon this will make the Vertibird instantly explode no matter what as long as you hit it.
Although the Washington Monument appears to be right behind the metro station hazmat disposal site L5, it is actually much farther away, and not even in that direction.
In the south-east, a burial mound containing search party log #1 can be found. After exiting Irradiated metro, turn right and the grave is in front of the last house on the right side of the street.