Vault 120

Vault 120 is a Vault-Tec vault located underwater in the Commonwealth. It would have been involved in the cut quest 20 Leagues Under the Sea.

Background
The vault was 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). Based on these unused cells the vault would have included an airlock, a research station, and "Stellwagen Gorge."

Behind the scenes
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.