After putting the Vault construction crew out of their irradiated misery, the Sole Survivor is sent on a chase through the tunnels dug beneath the Commonwealth, to activate more Vault-Tec workshops.
Activate the Vault-Tec workshops of the East, North, and North-East sectors. The order in which they are activated does not matter.
Use the workshop mode to strip the rubble on the eastern exit from the rail yard.
Navigate the tunnel to reach an alcove on the south wall, grab the control board and install it in the Vault-Tec workshop further east. There is a nest of mirelurk down this way, including a mirelurk queen.
Head back to the main cavern of the Vault and scrap the rubble blocking both tunnels in the north.
Head down the tunnel closest to the Vault entrance. A group of mole rats has tunneled into this section. After wandering through the spiraling tunnels, one comes to the Vault-Tec workshop for the North sector; the control board that activates it is on a cabinet in the metro station to the west.
Once activated, the nearby limestone wall can be removed to expose a deathclaw.
Continue east from the north sector to the North-East sector; the control board that activates this sector is up the incline to the east, through a small cave. Reach it by heading up the slope that leads to the workshop, then further upwards through the tunnel. The board is down the stairwell in the back.
Once activated, the nearby limestone wall can be scrapped to expose a radscorpion nest.
Return to the main area and scrap the rockslide to access the East Sector. Find the control board in the small room adjoining the train tunnel, then use it to activate the workshop (mind the mirelurks).