Vault-Tec Headquarters

The Vault-Tec Headquarters building is located in the Vernon Square area of the Washington, DC ruins.

This was Vault-Tec's base of operations around the DC area (it is unknown if this was their main headquarters). From this location (specifically, from the Vault-Tec Mainframe), you can learn where Vaults 87, 92, 101, 106, and 108 are.

Enemies
The only resistance inside the building are the leftover security robots and a few turrets. The models inside are: Protectron, Sentry Bot, Robobrain and Mister Gutsy. Also, there is one special model of the Robobrain on the level where the Mainframe is. It is called the Masterbrain and is hostile towards you. You can turn it off (and every other security bot in the facility) if you access three terminals that are placed around that area.

Super Mutants have also been found fighting the robots in the Guest Relations area. It seems they have been using the Vault-Tec HQ as a massing point, as Gore Bags which are a common find within Super Mutant bases are located in the Guest Relations mens restrooms.

Items
On the top floor there is an issue of Grognak the Barbarian on a desk. There is also a Big Book of Science on the second floor on the top of an isolated bookshelf against the wall across a destroyed floor. In the Guest Relations room there is a Tales of a Junktown Jerky Vendor book on a table up the broken stairs on the right side of the room.

Trivia
Over the front desk right when you enter the building, suspended from the ceiling is Vault 101's door, as an example of Vault-Tec's technology.

On the Administration level there is an employee computer in which you can order Vault-Tec accessories. Upon selection of an item, the terminal will say that the item's cost has been deducted from the employee's salary. It is unlikely that you can acquire those items. When you select "Vault-Tec Bobblehead", it outputs: "Only Available to Executive Level Employee." While this may lead you to believe there is a Bobblehead located in the building, there is not.

Bugs
Some people have reported that getting to open the doors to the Vault-Tec Mainframe does not work for them, i.e. selecting the proper command on all of the three terminals still does nothing to the doors, they remain shut. There is an alternative way to reach the Mainframe. The player needs to jump on the pipes that are found in the corners around the computer room below the Mainframe access. From the pipes, jump on to the big computers, and walk up as close to the Mainframe as possible. The option to interact with it should appear. If you stand on the bottom level just under the door that is stuck shut, the corner on your immediate left will have an extra pipe sticking out so you can be one step higher when you try to jump up. (Once you are up on the top pipe, face out and hop to the server on your left side...)