Vault 81

Locate the entrance to Vault 81 in a cave on the cliff face to the west, north-west of the fenced-off trash heap.

Activate the Vault Control Terminal. A security guard will question you via intercom.

The Overseer will then speak to you, offering two options to gain entry:

Provide three Fusion Cores. (You can find four at a time in Ammo Boxes).

Succeed at a hard speech check.

Once inside, you'll meet the Overseer and have a conversation. After she leaves, you'll have freedom to roam Vault 81.

Talk to Neil, who dreams of going outside.

Speak with Miranda, who has a different view on outsiders. You can succeed at a moderate speech check by asking “Something happen?” to learn about her past indiscretion.

Head west through radiation scanners and a doorway, then take an elevator down to the lower levels.

In the lower level, head north to find a shop run by Alexis Combes. You can talk to her about her relationship with her husband, Holt. Succeed at a moderate speech check by saying “Tell me” to learn more.

Peruse Alexis's wares, which include the unique Combat Rifle, Overseer’s Guardian.

Go north down a tunnel in the north-western corner, follow it upstairs past a security checkpoint to the Overseer’s office.

You can hack the Overseer’s Terminal [Advanced] to learn more about the vault's problems.

Backtrack to the main chamber and head downstairs. In the south-western corner of the lower level is the cafeteria.

Talk to Maria and Mark Summerset, who are more welcoming of outsiders and will mention that Vault 81 needs outside help and is struggling to stay operational. You can buy food and alcohol from Maria.

Head north down a long tunnel to reach the residential area.

Explore the living quarters for minor loot.

Down a tunnel to the north is the reactor room. Make your way downstairs to the west to find Old Rusty, a Mr. Handy maintaining the reactor.

Find Bobby and Tina De Luca. Tina wants you to stop selling her brother Jet. Bobby offers 75 Caps per dose. Do not sell him Jet to help him later.

If you have the Hacking perk, you can hack the Old Overseer’s Terminal [Master] in a small structure to the east to uncover secrets about Vault 81's true purpose.

In the south-eastern corner of the residential area is Horatio's barber shop. For 15 Caps, you can get a haircut, style, or color.

Ask Horatio for rumors to learn about an unfaithful husband, a Jet-addict, and a runaway cat, which starts the quest “Here Kitty, Kitty”.

Grab an issue of Taboo Tattoos from a table along the western wall.

Find Erin Combes wandering around. Ask her about her cat. You can pass an easy speech check to get a Teddy Bear, extort her for her Kickball, or shake her down for a Silver Locket. Agree to help her to progress the quest.

Head into a laboratory to the north-east to find Doctor Penske, who wants to use you as a test subject for her experimental fruit.