* Warning! Contains puzzle spoilers! *
When you start the level you can look at the security camera (TV) to see a sequence of numbers visible. This is the code for the 3 door keypad
I'd recommend heading to the far right area first to interact with the Gramophone to unlock
Once that's done, head to the elevator (doors are open) and press the keypad area. It only travels between the basement and the floor you are currently on. In the basement area, collect the gun from the locked body storage in front of you by solving the bloody keypad puzzle and return upstairs.
If you progress further into the locker room, there is a thing that will kill you if you wish to work on
Load times are a serious drag so I'd recommend playing the game 1st, then getting additional deaths as necessary.
Unlock the 3 door
and turn left. There's a watermelon you can 'pick up' with
. Lift it in the air a ways then click
again to unlock
Now that you've unlocked that - continue heading straight (leave the bathroom for now, its got a puzzle in it) and follow the only available path all the way to the end. In the last room on the left you will find the key you need to progress. You can head to the previously locked 2 door back at the beginning of the level to leave or enter the bathroom to grab ammo for the gun you found.
If you enter the bathroom, you will be locked in once you pass the doorway. Head in and on the far wall are a series of levers and buttons. Solving this will open the door.
It stays open once completed.
Enter the previously locked 2 door and climb the stairs. Follow the path around and the level will end before you reach the last doorway.