The Pitt Underground

The Pitt Underground is an area in the Fallout 3 DLC The Pitt. It can be accessed in The Pitt's Steel Yard, near a wrecked train entering an inaccessable metro tunnel.

Layout
The doors in the floor between the Underground and Uptown can only be opened if you assist Werhner. In this case, the "broken terminal" becomes functional and allows the doors to open. During this point in the quest, you unleash the trogs onto Uptown/Haven much like you would unleash the feral ghouls upon Tenpenny tower. If you do not assist Werhner, there is no way to open these doors.

Others have found just by releasing the Trogs by turning off the power to the lights and continuing along the same path you came in by, the doors up to uptown are found already open without any further imput from the player (360 version).

Enemies
There are about a dozen Trogs in the area, coming in groups of 3 to 4, with the occasional individual popping up out of nowhere (possible spawning). There is one instance of a massive group (4-5) spawning in pursuit of you as you reach the bottom of a ramp. Inside the sewer, two trogs can be seen canibalizing some unfortunate person from behind some bars.