Vault 74

Vault 74 is one of the Vault-Tec vaults. The vault was not mentioned in any game and only appears in the game files of Fallout: New Vegas.

It was originally made by Bethesda Softworks developers for the official Fallout 3 G.E.C.K. tutorials. Despite not actually appearing in the game file of Fallout 3, it strangely appears as cut content in the game files of Fallout: New Vegas, although is only accessible through the use of the console commands.

Background
Many Fiends live in this vault.

Layout
Vault 74 is small, consisting of just an atrium, a clinic, an overseer's office and no living quarters.

Related quests
The vault comes with a simple quest called Exploring Vault 74. You start the quest by simply entering the vault (by the use of console commands) and you complete the quest by taking the Vault 74 Overseer's log:

Appearances
Vault 74 appears only in the game files of Fallout: New Vegas. Due to its original nature of being a test demonstration, it is most likely to be considered non-canon.