As soon as DOOM Eternal is begins, just before starting the first mission, you can already see the Fortress of Doom, in which the VEGA AI and a large amount of material for the Doom Slayer reside.
This solemn and solitary place will serve as a base between missions. You can walk around it to admire the collectibles found during the missions, as well as to unlock additional rewards.
The fortress doesn't count as a mission in the menus, unless you are at a point in history that forbids you to return to the fortress, clicking "Continue Campaign" will take you back to it, even after you have completed it.
List of items to collect
- 5 Praetor suit points
- 3 Sentinel Crystals (1 available directly and 2 locked)
- 1 Codex
- 2 Cheat codes (secrets)
- 2 Weapon mods