As a homage to the originals, every level in Doom features a small hidden room based on a classic map from Doom or Doom II. To access it, you'll need to find a hidden switch to open it up, but once you enter it for the first time the full map will be added under the campaign main menu. Follow our guide and you'll soon have all 13 classic maps available to revisit at your leisure.
After dropping down to the lowest area in the opening section, spot the secret door then look for a hidden switch on the right to the side of a storage tank. Pull it then move forward through the now open doorway to unlock Doom II - Entryway.
Once you've opened the Maintenance Bay door and dropped down, find the secret door then go up the stairs to your left and climb up onto the crane. Go past the armour pick up and climb up to the next area to pull the switch, then go through the doorway below to unlock Doom - Hangar.
After clearing the first Gore Nest and entering the main foundry area, hang a right along the next walkway then look over the railings to your left to find the switch. You should see the door open straight ahead of you at the far end, so head there to unlock Doom - Nuclear Plant.
When you've crossed over to the far side of the opening area, look for the switch hidden behind some barrels. Next, go up the stairs to the right then through a corridor full of bodies and pentagrams to spot the open door which unlocks Doom - Toxin Refinery.
During the second section of the tower climb, you need to activate the Capacitor Pods - after hitting the button, go to the opposite side of the tower and ride the pod to the top where you'll find the switch on top of the docking point. Now ride the pod down to the bottom and wait for it to move out of the way, revealing the door behind to unlock Doom - Halls of the Damned.
After an arena fight with some big demons you'll see a green door ahead, then turn around and enter the cave behind you to find the hidden switch. Now drop to the lower level to the right as you face the green door and look behind you to unlock Doom - Slough of Despair.
At the start of the chapter during the climbing section, you'll reach a platform with several crates on it and the switch is hidden behind them. Pull it then drop to the level below to find the door behind a pillar which unlocks Doom II - Underhalls.
After meeting Sam and defeating the wave of demons outside the airlock, jump your way across the chasm and aim for the pipes on your right. Climb up to the top of them then jump/crouch to reach the switch on the other side of the fence - alternatively you can climb round the outside of the pipes. Once pulled, work your way back to the previous area outside the airlock where the door is now open to unlock Doom - Phobos Lab.
Once you've passed through the sacrificial altar room late in the chapter, you'll enter a room with a hole in the middle. Turn right at the bottom of the stairs to find the switch, then drop down the hole to find the door that unlocks Doom - Tower of Babel.
After opening the yellow door and clearing the next area, ride the moving column up to a skull switch then return to the yellow door entrance where a secret opening revealing the switch has appeared. Pull it then go back through the yellow door and down into the lower area to find the door to unlock Doom - Phobos Anomaly.
In the area early on where you get the yellow skull, look in the alcove to the right of the teleport out of the area to find the switch. Once activated, the door you came in through will open, then follow that corridor to reach the door that unlocks Doom - House of Pain.
In this area you'll find a hatch you can open to drop to a lower level, where you'll find a blue keycard. Once you have it, go through the blue door then left into the room and through the other blue door, where the switch is hiding behind some crates. Now go back through the first blue door and to the far end of the corridor to find the door to unlock Doom - Command Control.
After laying the first Wraith soul to rest, go down the right hand stairs (as you look out from the platform) to find a skull switch. Activate it, then turn right at the bottom of the stairs and head into the tunnel ahead. Follow the blood up the stairs to the switch, then pull it to reveal the final door next to you that unlocks Doom - Pandemonium.
Congratulations - you've unlocked every Classic Map in Doom.