On this page of our guide to Doom Eternal we explain how to reach the question mark that levitates high in the air in the Fortress of Doom. It is one of the game's greatest secrets and you have to complete the campaign in 100% and earn one of the trophies if you want to unlock it.
The question mark is shown on the map of Fortress of Doom. It's located very high, in the top part of the Fortress. It is located above the room adjacent to the captain's bridge.
The described question mark can be spotted under the ceiling and it seems unreachable.
Become interested in the stained-glass in the room with a question mark. There is a button next to the stained glass - we have marked it in the screenshot. Shoot at it with any weapon.
Hitting the button activates the red launcher pad shown in the picture. Stand on the launcher pad and jump in the air.
You can reach the area with the question mark from the above. It will be a floppy disk with a cheat code for a fully upgraded Praetor Suit.