Step 1: Insert N31L's Head
Before the player can gain access to the outside world, the player must locate N31L's head, which is located on the catwalk above the Water Treatment plant, and can be accessed by dropping onto the green ledge within the hole in the Ops Center. Once the player has obtained N31L's head, the player can insert it into the computer terminal within the spawn room, where N31L will turn on the power.
Step 2: Opening the Portal
Once the power is on, the player must go to the Cargo Bay and press the button on a pole to the left of the main door after they enter the room. After it is pressed, a laser turret will come in from another room and shoot at a halfway closed door on the other side, revealing a portal. Entering the portal will bring the player to the theater, where the achievement will unlock.