DOOM + DOOM II

if you are doing this on Xbox you will need to plug in a keyboard to type in cheats

Boot up "Legacy of Rust" go to Level Select and choose the level E2M7 "Brink" difficulty doesnt matter as we will be using the God Mode cheat (i left it on Hurt Me Plenty)

When you spawn in start typing the cheats

Type in "IDDQD" for God Mode
Type in "IDCLIP" to be able to Clip (walk) through walls
Type in IDKFA" for max ammo for all weapons and all Keys

When you have activated all the cheats, you will see green walls with faces on them, clip through the barrier in front of you and you will drop onto the green floor, walk into the faces on the wall and you will clip on a path next to the bridge, walk over the bridge and keep moving forward, you will get to a room that looks like an Arena with a hole in the middle, just keep walking forward and you will see a skull on the wall infront of you. Keep walking through the walls and up the stairs infront of you and through the door. Same as before with the Arena room keep going straight forward through the wall, past the room full of ArchViles and you will be in a room that has a huge machine infront of you. Keep going forward and up the stairs you will see "one dead Space Marine" infront of a console and switch, activate this and you will end the level and the achievement should pop not long after

Start a new game in Legacy of Rust

Type IDCLEV27

IDDQD god mode, IDKFA for full inventory, and IDCLIP so you can head straight north through the walls until you find a portal you have to activate to end the level.