Secrets are everywhere in Doom: Eternal. Many of them are scattered all over the campaign's maps, and thankfully developer id Software made many of them easy to find by using your mini-map in your menu. However, there is also a handful of them in the main hub area, on the Fortress of Doom. Not all of them are labeled, such as the ability to play the classic Doom and Doom 2 from your personal computer. To play Doom 2, it's much easier to unlock than Doom. All you have to do go down to the second level of the Fortress of Doom, choose the right file and type in the code: FLYNNTAGGART. Immediately after typing it in, Doom 2 will pop up on the computer screen and you can start playing it. To start playing the classic Doom, you need to put in a bit more work. You can only gain access to it once you have collected the 14 different cheat codes, shown as floppy disks on your map. They are scattered all over Doom: Eternal, so you will want to go through the entire game's campaign to obtain all of them. If you miss any, you can always choose the mission select screen found at the top of the Fortress of Doom to repeat a mission. Including the classic Doom and Doom 2 games in Doom: Eternal is a great way to have id Software share its history with modern players. Those who may have never played those games now have an opportunity to do so, without an additional price tag.