Doom Eternal is already a love letter to the series in many ways, but it actually contains the first two classic games in the series as an easter egg. Both games, Doom and Doom II: Hell on Earth, are fully playable within Doom Eternal, and they’re not too difficult to unlock. Here’s how to play classic Doom games in Doom Eternal.
How to Play the Original Doom
In order to be able to play the original Doom, you first need to unlock all the cheat codes in Doom Eternal. You’ll have to collect all 14 floppy disk collectibles throughout the game’s main campaign in order to do so. Because there are cheat code floppy disks on just about every mission in Doom Eternal, you’ll also have to complete the main campaign before you can start playing the classic Doom game. Once you’ve completed your floppy collection, however, head back to the Fortress of Doom and make your way to the Doomslayer’s room. It’s in the lower portion of the ship, and you’ll know you’re in the right place if you see the guitars on the wall.
There’s an old school computer on the desk. Interact with it, and if you’ve met all the requirements, you should see an icon for Doom on the left side of the screen. If there’s still an icon of a floppy disk with a question mark on the left side, you’re missing some cheat codes. This version of Doom is actually The Ultimate Doom, the final version of the game released in 1995 that contains several additional levels.
How to Play Doom II: Hell on Earth
Doom II is much easier to access. You don’t have to complete the campaign or find any collectibles to play it. Instead, playing Doom II only requires a password. Head the Doomslayer’s room in the Fortress of Doom and interact with his old computer. Select the square on the right side with the floppy icon and question mark. You’ll be prompted to enter a 12 character password. Enter FLYNNTAGGART. Doom II should then boot up and remain unlocked at the computer.