Key Bridge

 is the big bridge that crosses the river Potomac north of Jefferson Memorial, from The Citadel in the direction of Washington Monument.

Quests

 * The bridge is used by the Brotherhood of Steel in the quest Take it Back!, in order for Liberty Prime, Brotherhood Soldiers and Lyons Pride to get across.
 * This bridge is also a part of the mini-quest Protecting The Water Way, where you find the Bandits, who have a holotape on their corpse revealing their hideouts location.

Inhabitants

 * On the west side, under the road, is a Raider base.
 * Under the bridge on east side is a Scavenger (trader).
 * North of the east side of the bridge is another Raider camp.
 * On the east side, near Irradiated Metro is a Super Mutant hideout.

Notable loot

 * North of the bridge, east end, between the Scavenger and Raider camp, is a grave with Search Party Log #3 for the Searching for Cheryl unmarked quest.
 * A copy of Duck and Cover! is on the table in the Raider camp on the east side of the river.

Bugs

 * On the west side of the bridge, there is a way to get out of the level by jumping on the rocks just left of it, from there you can walk "under" the Capital Wasteland and even get into the Citadel from very early in the game (allowing you to get Power Armor Training before the quest "The Waters of Life")

Appearances
appears only in Fallout 3.