E1, M2: Nuclear Plant
This level has 6 hidden areas. A gameplay video with all the secrets is included at the end of this section for those that prefer to watch and learn.
Secret 1
When you head to the right from your starting position and head around the corner, you will see a patch of wall to the left that looks different. Open it to find the first secret area with some goodies and a switch. Be sure to toggle the switch!
Secret 2
By pressing the switch, a door will open in the room across from the first secret area, granting you access to the courtyard and all of its items and bonuses.
Secret 3
In the flashing computer maze is a green armor. The wall behind it will open when shot at. This hidden passage leads to the chainsaw and a number of extra items.
Secret 4
Inside secret 3, in the passageway leading to the chainsaw is a bit of silver on the wall. The section of wall next to this opens like a door to reveal armor bonuses.
Secret 5
On the Eastern side of the flashing light maze is a small area of wall surrounded by two silver things. You can open it to reveal a secret area with a backpack inside.
Secret 6
Right before the platform that will take you down into the room of imps, there is a charred-looking body on the floor in front of a piece of wall that looks different from the pattern around it.
Here’s a video walkthrough of all the Doom secrets on this floor!