Vault 81 (quest)

Vault 81 is a quest that can be obtained in the Commonwealth Fallout 4. Its completion is required to access Vault 81 if you don't possess a high enough persuasion level.

Synopsis
The Sole Survivor, as they travel across the Commonwealth wastes, stumbles across a still active vault, with a peaceful community residing inside.

Walkthrough

 * 1) Upon attempting to integrate with the Vault 81 door, the security chief will contact the Sole Survivor through the intercom system, and will ask for their intentions. Upon convincing the security chief to open the door for the Sole Survivor, the overseer will use the intercom to tell the Sole Survivor to report directly to her. If you cannot persuade security to let you in, you're tasked with bringing them 3 fusion cores instead to enter.
 * 2) Speak with Overseer McNamara, and after speaking with her, the Sole Survivor will gain nearly limitless access to the vault.