Vault 21 Vault 21 is a Vault - Tec vault that was once hidden under Las Vegas , Nevada . It has since been converted into a hotel / casino and acts as one of many sources of income for Mr . House and his young New Vegas empire . Background . Located in downtown Las Vegas , Nevada , Vault 21 was a unique Vault experiment : everyone in the vault was equal , it was created with a perfectly symmetrical layout , and the dwellers settled their differences via games of chance . Reliance on luck to solve problems created what might be considered the perfect realization of anarchy : a society in which everyone is equal and no one has an advantage over the others . Vault - Tec ensured that every person admitted to the vault when it first sealed was a compulsive gambler and were unable to decline when Vault - Tec personnel running the vault informed them that this was how the vault was to be run . The original dwellers then passed on their lifestyle to their children and so on . However , as with all utopias , the peace was not lasting . Sometime between 2271 and 2281 , Robert House planned an occupation of Vault 21 . Resisting attempts to be assimilated into his empire , the inhabitants agreed on gambling to settle the issue . The game they played to settle the deal was blackjack and almost the entire vault was in attendance . In a risky bet , the supporters of House won against the opposition , and Vault 21 ' s interior was stripped of its useful electronics and equipment and partially filled in with concrete , forcing the dwellers to resettle in the wasteland and on the Strip . At Sarah Weintraub ' s and Michael Angelo ' s ( a . k . a . Sheldon Weintraub ) insistence , House left the topmost level intact and allowed the Weintraubs to establish a hotel there , which became another source of income for his fledgling empire . Vault 21 is one of the extremely rare experimental vault s which successfully protected its inhabitants while fulfilling the parameters of its experiment . The experiments in most other Vault - Tec vaults ended up killing or permanently altering their inhabitants or forced the dwellers to abandon . Although Vault 3 was a control vault , intended to recolonize the surface after an extended period of time , when its door was opened the Fiends slaughtered its residents and took over . Layout . The vault ' s main blast door has been transformed into a sign advertising the vault / casino . " Vault 21 " is emblazoned on it in neon lights . The vault entrance is an above ground building which contains the Vault 21 gift shop . It is run by one of the only two native residents to have remained , Sarah . Stairs lead from the gift shop down into the vault . The vault has been converted into a casino and hotel . There is a central atrium with gambling tables , a hallway with living quarters , including Sarah ' s room and a guest room that the player can rent . Another door leads to the cafeteria / diner . The lower levels were filled with concrete by Mr . House and are inaccessible except for the maintenance level , which is accessible from the basement of The Tops , where the Chairmen appear to have tried to break in . This level consists of a long hallway with a few small rooms branching off of it . The elevator in Benny ' s suite leading to it is locked unless he is attacked in the Tops Presidential suite , and the tunnel ends in another locked door . Appearances . Vault 21 appears only in " " .