You'll eventually find a small office with the code posted alongside several sketches on the left exterior wall.
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Code #48 - Leave the room with the lockers and go right.Gold Robot - When the golden elevator takes you to the vault, search it to find the little robot.Chapter 7 Gold Ashtray - When you reach the well in the sewers, go to the right and jump down to the opening of a small pipe.Code #47 - Leave the room and continue past the charge station until you reach a room with red lighting and lockers.Letter #10 - In Chapter 15, go upstairs and search the rooms near the pillar until you find the letter lying beside a bed.Code #24 - When you reach the area with the satellite on the rooftop, enter the small room left of the stairs and grab the code from on top of a chair.Code #42 - Next, go through the door and fall through the hole in the floor.Gold Rabbit - Before you hit the checkpoint, you'll pass a robot cabin.Pass the barred doors for now and go into the next room on your right.In the room, the code is on a trolley to your right.Put the retrieved files in the drawer.Code #49 - In the room with the computer screens, while you're trying to raise the buoys, go to the left side of the room and climb the stairs up to the catwalk.If you interact with the character to your left, you'll get the dagger.Go inside and head right to find the medallion on a table near the bookshelves.Gold Knife - In that same area, go upstairs and right, into a new room.Letter #9 - In Chapter 13, during your search for the space suit, go to the northern side of the building and enter the decontamination chamber.There is another metal fence for you to cut chase rewards card through on the other side.Stealth and the Environment When you're using stealth, make sure to take the environment into account.Make your way to the platform near the yellow pipe, and then go left and drop down to a new area.
For example, you can usually find a place to hide to wait until the guards pass you.
Go through the shaft into the left office to find the next code.
Walk across the beam into the next area, cut through the grill, and cross the crates to the left to find the compass.