As soon as you start Doom Eternal you will be immediately dropped on to earth, ravaged by a demon invasion by 3 hell priests. Luckily you are already on the tail of one, you are the doom slayer after ...

The first of the game's Cheat Codes can be found near the end of the level. Walk through the corridor in the image below, and you'll see a yellow question mark hidden behind a gate above you. Continue ...