Vault 76 gives Fallout 76 its titular number, but there are other vaults in post-apocalyptic West Virginia, and at least some of them will open up after the game launches. Bethesda has teased what to expect from future updates to the online Fallout, and among myriad other additions we'll see "new Vaults opening."
There's no official detail beyond that, but the beta has offered a few hints about what to expect. Players have managed to clip into various vaults strewn about the map, and it looks like they're already at least partly complete.
Vault 63, for example, includes an 'emergency management terminal' that you can access for an unspecified mission. It warns that once the mission is accepted, "the Vault Door will cycle, and no further personnel will be itted in or out of the Vault until the operation has been completed."
The exact role of these vaults remains unconfirmed, but the phrasing on that terminal suggests it might give access to some sort of instanced dungeon-style content. You can see those vaults for yourself over on Reddit.
Bethesda's pre-launch Fallout 76 release date.
Today has also seen the reveal of the Fallout 76 release times, so you can follow that link for details on exactly when you'll be able to play as the game launches later this week.