How to unlock: after reaching the Vault 81 (M6,3).
Once you enter inside the crypt, try to open the door by using the Pip-Boy. The security will answer and, after short negotiations, they will agree to let you in. However, first you must deliver 3 Fusion Cores.
Example locations from Sector 1, where you can find the cores without having to fight powerful enemies:
- USAF Satellite Station Olivia,
- Bandits' camp under the Lonely Chapel on the southwest of the Sector,
- A small cave hidden under the gas station (where you have found Dogmeat) in front of the Concord.
Quest rewards: Experience, 100 bottlecaps and access inside the crypt where other quests are available.