The offices are on two levels, spread out around a single east to west corridor. There are several entry and exit points. The usual entry is from the visitor center by way of a short walk through the top tier of the Hoover Dam Power Plant 01.
Cassandra Moore's office is the first door on the right when coming from Hoover Dam Power Plant 01.
To the north is a hallway that leads to the lower level. There is a small bathroom with empty lockers just before the stairs down.
The rec room is north central of this western area. There are signs on the walls that point to this location.
Just past the rec room on the south side of the corridor is a door to a small laboratory. Colonel Moore can sometimes be found in here if she is not in her office.
Just past the rec room on the north side of the corridor is a small room that leads to an exit door to the second Hoover Dam Tower on the NCR side.
There is a radioactive storage room in the southeast corner of the western area that contains two Chinese stealth armor suits.
Between the east and west areas, off the main corridor, is a large door to the dam control room center, which is filled with racks of electronic equipment. Every desk in this room contains a Hoover Dam Saferoom Key, along with random loot. This is the control room you are sent to by Mr. House in All or Nothing.
Going south along the corridor that loops around the eastern section of the offices leads to a small storage room and the theater/briefing room.
There is a locked door that requires a key in the extreme southeast corner of the area.
Going north along the corridor that loops around the eastern section of the offices leads to a small kitchen. At the back of the room is an exit door to a Hoover Dam Tower on the Legion side of the dam. It is locked or unlocked depending on what quest you are on.
The first door on your right when coming downstairs is the armory. Quartermaster Bardon can be found here.
You can get downstairs by heading west from the door to the middle tier of Hoover Dam Power Plant 01.
The rest of the level is two large dorm rooms where the engineers bunk down.
Fixin' Things - walk the hallway north from the Hoover Dam Power Plant 01 door. It's on the floor next to a toolbox and Altmetall where the hallway makes a right turn.
Programmer's Digest - follow the same right turn to reach a small chemistry laboratory on the right. The book is on the desk beside a computer terminal and a pair of eyeglasses.
Two Chinese stealth armor suits - If you read the notes on a terminal in a small office across from the rec room, it refers to these suits and then states that they were lost when everything was reorganized. These suits can be found in one of many wooden crates stacked in a storage room with radioactive barrels. You can find the storage room by traveling north from the door from the Hoover Dam Power Plant 01 door to the first corner, east to the next corner, and south to the next corner. The door is on your right, at a dead end. If you hug the left wall when entering the storage room, you won't get any rads and the crates are right in front of you on the back wall. (You will lose Karma)
Hoover Dam Saferoom Key - one found in each of the three desks in a large T-shaped room between the central and eastern wings of this area. Opens a saferoom in the second floor of the visitor center that contains nothing of interest.
Depending on which quests you have active and what state they are in, various doors and elevators may be inaccessible or locked requiring a key at one point and open and unlocked at another point in time.