General hints:

* Look for "Munition" compartments for supply of ammo.

* The "Office" contains the screen showing the location of all secrets. Not quite spoiler but close. 

Key hints:

* Location of keys are identified with colored screens pointing to either the location of the key and/or switch to be activated.

* The yellow card screen is in the "Gestapo" room, the blue is near the Drinking Fountain and the red is in the "U-Bahn" station of the Kraft Werk.

Combination hint :

* The code for "Schalter 5001" can be found between the shower room and the Gestapo room in two separate locations. 
