There are loose ends that must be tied up before the entire story of Shay Cormac is finished. You wake up at the office and your manager asks you to go down to the basement to fix one more server.
Go to the elevator and head down. You’re given Level 3 Security Access, which opens all of the remaining doors in the building. You can get the last of the Tablet Documents and the computers that are in the building (including the basement, which has both of those collectibles).
Follow the red emergency lights through the dark hallways, and pick up Tablet Document 17 on the northern side of the map. The server room is at the end of the tunnel, where you find a small service elevator. Take that down into the server farm, repair the system, and return to the platform above. Use the terminal up there to make an important upload, and then return to your cubicle.
Using your terminal unlocks the achievement/trophy “Sending a Message.” It also takes you to the last of the fragmented memories.