Where to find saltpeter in Amnesia: Rebirth

During the passage of Amnesia: Rebirth, you will encounter many puzzles, and for one of them you will need saltpeter

Saltpeter is one of the three ingredients needed to create a live shell for the cannon of a tank stuck in a fortress. And if sulfur and coal can be found in the arsenal where the projectile itself is made, then to get saltpeter you will have to leave it.

Exit the armory, go to the green door and follow a little to the right, into the passage leading to the quartermaster's warehouse. You passed through this door when you were running from the monster. So go back there, go up the stairs to the left and go through a couple of doors. In the end, you will see a partly open storage room door ahead. There will be a rack with a canister of saltpeter! Don't worry, the monster is no longer here.

After picking up the saltpeter, return to the arsenal and pour it into the shell. Add sulfur powder with crushed coal there!