Once the raiders are dealt with, the Sole Survivor can activate the control panel using their Pip-Boy to open the vault door. After that, they can use the terminal inside or outside to open and close the vault door.
More building space can be unlocked by finding other control boards, one for each section. Once all of the sections have been unlocked, the vault becomes a seamless and expansive workspace, with the only borders being at the vault's door itself, in the subway, and the shop.
Vault 88 consists of a number of chambers and passageways. Initially the entranceway to the vault is available, filled with a number of leveled feral ghouls and Security Chief Andersen. Once the main area's workshop has been unlocked, the player may then access the main cavern of the vault, which is an expansive space filled with construction machinery, destroyed trains, and piles of debris. All of these can be cleared for open space.
In tunnels to the left of the main room's entrance as well as on the opposite wall, are huge debris piles and limestone walls. Each of these seals off another section of the vault, and once cleared will initially show a border where the workshop cannot access just yet.
After unlocking all of the workshops during Explore Vault 88 it is now possible to link each passage by clearing limestone walls. Sneaking cannot be activated while in workshop mode and it is possible to be rushed and overwhelmed by the enemies that wait beyond as soon as you clear the walls.
Starting from the main chamber, taking the northern-most passage yields three uranium veins on the way to the subway (14 nuclear material) or a limestone wall on the right. Clearing it reveals a passage containing a leveled legendary deathclaw. Clearing the second limestone wall beyond leads to the north workshop.
The northeast tunnel has a limestone wall tucked away behind the partial vault construction down the stairs, which connects up with the eastern workshop and the Vault-Tec water pump. Continuing north down the passage has a limestone wall on the left side, beyond which is a nest of seven radscorpions. Clearing the next limestone wall connects up with the northeast workshop. A rockslide to the right of the radscorpion nest entrance yields nothing new, but continuing up the passage to the stairwell gives more uranium (15 nuclear material). The barricade up the stairs can now be removed, freeing the feral ghouls beyond it and unlocking the University Point Pharmacy entrance. There is a barricade in the subway tunnel as well, which leads to a ladder emerging right outside Milton General Hospital.
The east tunnel contains a limestone wall with some radscorpions behind it and more uranium (38 total). A second limestone wall hides more of the same, with more radscorpions and many veins of uranium totalling 78 nuclear material. Another limestone wall on the right reveals a leveled sentry bot and 60 units of nuclear material. The limestone wall on the left has 56 nuclear material and a family of mole rats.
- The Vault 88 map marker replaces the Quincy Quarries one after listening to the Vault 88 radio beacon when the Vault-Tec Workshop add-on is installed.
- Provisioners that run supply lines to this vault will stop just outside of Quincy Quarries and never venture inside. However, trade caravans from Bunker Hill will enter the interior if a trading post is established there.
- It is possible for super mutants and other enemies to attack the settlement. Due to the spacious interior, it can be difficult to track down the assailants. And since the enemies have AI that isn't normally meant for attacking an indoor settlement, they will often loiter or wander aimlessly instead of actively attacking resources or settlers.
- The leveled sentry bot and some radscorpions have permanent corpses, and the former cannot be carried elsewhere due to its extreme weight (unless the sentry bot is hacked to self-destruct, which will allow its body to disappear).
- On PC it can be solved by opening the console, clicking on the corpse and using the command disable followed by markfordelete.
- Once cleared out, there are two back entrances, one near Fallon's Department Store, and the other near University Point.
- If you decide to kill Overseer Barstow, the buildable experiments can be unlocked by looting her body and retrieving a paper marked as a quest item. This actually skips the "testing" phases of the experiments.
- Killing Overseer Barstow will not reward you with the legendary vault suit.
- The layout of this vault is specially designed for building a vault. The floor is set to the proper heights for the sections making the "snap and build" easier.
- When dismissing a settler they will walk towards the exit, if in the main cavern, but will not register the additional highlighted but immovable segment of the Vault hallway, making them unable to leave until you "wait" or travel somewhere else.
- Settlers living in Vault 88 will say the same lines as Fallout Shelter Vault dwellers (ex. "I want to draw a picture later, any requests?").
- Vault 88 has higher settler limit than other settlements. It can house 10 more settlers than normal settlements with the same value of Charisma of the player.