As vaults go, the story here isn't actually the most heinous one. In fact, if you ended up in Vault 81 you could say you nabbed yourself a pretty good deal. The vast majority of Vault 81 residents are alive and well at the time you arrive there. The vault was used to try and discover a universal mega-cure for every disease in the world. The vault's overseer however, changed her mind at the last moment, deciding that she couldn't go through the unethical research (good to know at least one Vault-Tec employee is capable of compassion). Instead, the scientists carried out experiment on lab rats while the rest of the vault's residents went on with their vault lives, unaware that there even were experiments going on. In 2277, 10 years before the events of Fallout 4, the vault's overseer opened its doors for the first time, allowing for people to come and go, and for trade to happen with the outside world. The vault is just south-west of central Boston, and you can visit the vault with relative ease, discovering what happened as a result of the research to find a cure for all diseases...