Vault 74

Vault 74 is one of the Vault-Tec Vaults located in the Capital Wasteland. Not much is known about its fate except that it was overrun by raiders and deathclaws. It's small, consisting of just an atrium, a clinic, and an overseer's office. There are living quarters but the only way to open them is to unblock them via button in the overseer's office. Venturing further into the quarters information on project achilles is found along with "creatures" that killed most of the inhabitants in the quarters. The one who left these notes in the terminal wrote of how he was told to seal off the door to the quarters, being the only chance of rescue. This explains the blocked door. Immediately after this deathclaws appear, and you must destroy Vault 74 with a nuke within the vault. To do this you must go through a series of tunnels, eventually escaping through a ventilation shaft filled with ghouls. Afterward the mountain explodes and upon returning to the entrance you will find it buried under dirt. The state of disrepair in the Vault is most likely due to the fact that everyone in Vault 74 perished, and that the Raiders had raided and looted Vault 74.

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

Appearances
Vault 74 is a Vault that the Bethesda Softworks developers made for the official G.E.C.K. tutorials and it does not appear nor is mentioned anywhere else. Given that, the location is likely non-canon. This means that This Vault can't be found in any console versions of Fallout 3, only PC. This Vault also appears in the game files of Fallout: New Vegas in an incomplete state.

Related
Vault 74 Overseer