Vault 12

To Find vault 12: Free the ghoul prisoner (in the water shed) and he should tell you that the cell to the right of him is a manhole which leads to vault 12. Go down the manhole and you should easily find the vault entrance.

A Vault-Tec nuclear shelter, Vault 12 was located under the town of Bakersfield, California, designed to house 1000 dwellers. It was not closed after the bombs fell, resulting in the ghoul town of Necropolis.