The main entrance is via a metro station entrance located northeast of Bethesda office east. Uncharacteristically, this station doesn't have an obelisk marking its location.
Inside the station, the mezzanine and platform are relatively intact. Subway tunnels are destroyed and access is limited to the tunnel openings. The subway tracks ran north to south. Located off one of the destroyed subway tunnels, there is a service tunnel which leads to a sewer grating ladder. This sewer grating is located south of Bethesda offices west. This station is irradiated by containers of radioactive waste. The largest concentrations can be located on the platform and near the sewer grating ladder.
The underworks are populated by the feral ghouls. It is not surprising to see a glowing one or a feral ghoul reaver (if Broken Steel is installed) here among the other types of ghouls. Upon entering, the player may be swarmed by all the ghouls at once, forcing the player into a fight with around 6 ghouls of varying difficulty (depending on the player's level).
The feral ghouls and raiders will often start fighting amongst each other if you fast-travel to this location.
When entering Bethesda underworks for the first time while wearing the Ghoul mask, all the ghouls except one glowing one will run past you and exit the underworks. They will go to a specific area in Bethesda Ruins and stay there.