This Amnesia: Rebirth walkthrough will cover The Fortress. This is the sixth location you will come across in the game immediately heading up the Desert Path.
Amnesia: Rebirth The Fortress
Elevator Room Puzzle
Go through the big door and enter the courtyard. There will be a big door to your left that has a light on.
Enter it and you will find a radio inside from which you can hear Doctor Metzier’s voice.
Take the matches from the barrel to your right and then grab the oil on the stool behind you.
You can now light your lantern. If you need more matches, then collect them from the crate in front of you.
The door up on your right will take you to a hallway with an elevator at the end. It is missing two pieces that you must find in order to make it work.
The first item is a winch. Head straight from the hallway entrance and continue until you come to the area in the back-right corner with a Ballista.
The winch is there, so take it and head back to the elevator.
Put the winch on the box, close it, and rotate it. Now you need to attach the wooden platform that is next to the elevator. The elevator will be able to take you up now.
Accessing the Quartermaster Room
The main door will be locked. There will be a crack that you can move through to get to the area with the wheel and cannon.
Attach the wheel to the weapon and do the same with the second wheel. Roll the cannon into the hallway and put a hole in the floor.
Drop down to use the radio, then access the Quartermaster’s Office from here. Grab the Saltpeter while you’re in the office since you’ll need it for a later objective.
You will learn your next objective here. You need to search for the rest of the survivors in a village outside of the fort.
Leaving The Fortress
There is a tank in the courtyard. Head to it and enter it via the gunner door. Grab the key and go towards the Fortress entrance.
There is a room to the right of that just by some stairs so go inside.
This is an ammo room where you are able to make gunpowder. Start grinding charcoal and take the sulfur from the locked room.
The key can be found next to the body. Add the materials as well as the Saltpeter you collected earlier to the mixer. This will give you a tank shell.
Head back outside, load the cannon and fire a hole in the door to escape. You will then be able to leave the Fortress in Amnesia: Rebirth.