This achievement is possible once you reach the
Sewers.
You will proceed through the Sewers, and pick up a
T-bar, which is mandatory in order to make progress through the game. Also, make sure you grab the
Sewers Key which is in
Sewers (Lower). Use the T-bar to open the door that leads to
Bottom Waterway, and find the key on the wall just before climbing the ladder down.
Now, head through the
Lower Waterway, and use the T-bar to gain access to the Workroom Lift. Once inside, take the elevator up, and find a roll of film on the table in the middle of the room labelled "Hiding Places" and pick it up.
With the film, we must return to the
Police Station. you have to head through the nearby treatment facility door, and move the shelf over to reveal a secret elevator up. Follow the paths up, all the way back to RPD, then go to the
Dark Room to develop the film.
With the film developed, we can get two secret items from these two new locations:
- Lighting Hawk Red Dot Sight -
STARS Office: small office, inside the desk drawers
- x400 Flamethrower Fuel -
Press Room: desk in the back left