Vault 120

Vault 120 was to be a Vault-Tec vault located underwater in the Commonwealth. It would have been involved in the unused quest 20 Leagues Under the Sea.

Background
The vault was to be placed underwater, based on untextured assets that can be found in xEdit of both an underwater vault window (VltSquidWindow01) and an underwater vault door (VltLGDoorMarine01). Cell names found in the game files of Fallout 76 reveal that the vault would have had an airlock, a research station, and that one level would have been named "Stellwagen Gorge."

Behind the scenes

 * Modder Ladle backported the unused content, their work can be found here.
 * Todd Howard discussed Vault 120 and the 20 Leagues Under the Sea quest in a Reddit AMA on November 10, 2021. He stated that it was to be a "Bioshock style vault," with a giant sentient octopus outside.
 * "Stellwagen Gorge" shares its name with that of the real-world Stellwagen Bank, an oceanic plateau in the Massachusetts Bay.