Underhalls (Doom 2016)

Underhalls is a classic level from Doom (2016). It is a recreation of Doom II's that includes enemies from the later game, but retains the original game's pickup and decoration sprites.

This level is unlocked after finding a part of it hidden in the Argent Facility (Destroyed) stage. Once unlocked, the full level can be played from the "Classic Maps" tab in the Campaign menu.

Essentials
In this level you start with the pistol, combat shotgun and rocket launcher.

Kill the three possessed soldiers ahead then cross the water trench and go up to a door that has two more soldiers waiting behind it. Turn left to find a third soldier guarding a switch that you can flip, then go back to the starting room to see that a gray barrier to your right has lowered allowing you to follow the water trench into a tunnel. Follow the tunnel round until you see some soldiers on a raised platform and climb it to see a brown building ahead of you, go inside and jump up the stairs leading to the red keycard - taking it will open two alcoves below that hold imps and a pinky.

Return to the starting room and go back through the door at the top of the steps, but this time turn right and open the red bars in front of you to get to another switch that will open another gray barrier in the starting area. Go through this second barrier and follow the tunnel round until you get to a gray wall, then turn right and right again to find some soldiers guarding a few barrels and two holes in the floor. Drop down the left-hand hole to enter a room with imps and more barrels, blow them up then go to the end of the rom to find the blue keycard. Return to the hole you dropped down and open the nearby blue door, quickly blow up the barrels behind it to dispose of more imps then follow the water to another blue door that leads back to the tunnel you passed through earlier.

Other points of interest
After entering the first water tunnel you will see some steps leading down to a UAC door. Behind it are many soldiers guarding a super shotgun.

Secrets

 * 1) At the top of the staircase inside the building where the red keycard is found, open the western wall just south of the alcove in which the key rests. Behind the wall, there is a small room containing several soldiers, a blue megaarmor and a teleporter leading back to the starting room. Using this teleporter may provoke the enemies that are released after taking the red key to infight with each other, due to their distance from the player.

Bugs
The wall which divides the red key and blue key areas from each other is supposed to lower after entering the east side of the water tunnel (in case a player wishes to backtrack). In the recreation this wall never lowers and the gap is too small to squeeze through, forcing players to walk around the entire water trench.