Atomfall has a lot of locked doors that require keys and keycards to pry open. One such door can be found near the Casterfell Dam at the Casterfell Data Dam Store, which is, unsurprisingly, located within Casterfell Woods. There, you’ll find a locked entrance to the B 887126 Control Room with no sign of a key.
That’s because the key was in the possession of someone who did not survive the disaster that occurred in the quarantine zone. If you want into that control room, you’ll need to loot the key off of their corpse. But in typical Atomfall fashion, this body won’t be conveniently placed. Here’s where you can find this key.

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Where To Find The B 887126 Control Room
To find the B 887126 Control Room, you first need to reach the Casterfell Dam Data Store. This is an important location as it can affect the endings for either Dr. Diane Garrow or Joyce Tanner as they both want information from a computer terminal within the Data Store. It can be found at the coordinates 22.5 E, 92.4 N on the map in Casterfell Woods.
Once you get there, you’ll drop down into a ruined area and find the entrance to the Data Store. Next to that entrance on the left is the B 887126 Control Room, which you currently won’t be able to access. So where could that key be?
How To Get The B 887126 Control Room Key
Across from the Casterfell Dam Data Store will be a tunnel that is full of toxic gas. On the other side of this tunnel is Bunker L9, which is where you can grab the Casterfell Woods Radio Tower Keycard. You can go through this tunnel from either the Data Store or Bunker L9 entrances, but regardless of where you enter, you should bring plenty of Antidotes along with you since the gas in the tunnel will inflict poison build-up. In fact, you should consume an Antidote before going in since it will give you poison resistance.
If you enter this gas-filled tunnel from the bunker side, be careful since there will be Feral enemies in the area. Ferals will also be inside Bunker L9 if you plan on grabbing the Casterfell Woods Radio Tower Keycard.
Once you’re in the gas-filled tunnel, you’ll find a body near some shelves. Loot the corpse, and you’ll find a note titled “The Proper Antidote” along with the B 887126 Control Room Key. Now you can exit the tunnel and head back to the control room. Use the key, and there will be items for you to loot. This will include a B.A.R.D. Crate with a Training Stimulant inside.
There will be a console with a lever marked Ventilation Override. Pull that and you’ll vent the toxic gas in the tunnel. Now you can go back into the tunnel and loot the rest of the items inside. You can also use it as a shortcut to get to the Casterfell Dam Data Store without constantly running into druids along the way.
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