Level 17: Processing Area
Back to Final Doom
From the Start turn around and open the white door. Inside you’ll find an Invisibility sphere.
Open the door to the main building and clear out all the enemies from the corridors and outdoor areas. They will wander around and come at you from all directions so you will need to quickly eliminate the hit scan enemies.
Once the coast is clear head east along the first hallway and open the wall to the south. This leads out to Secret 1, the walkway around the starting yard. Follow it around to the end where you’ll find a Super Shotgun.
Head east along the hallway again and this time go up the stairs. In the computer room you’ll find the Yellow Key.
Go down the stairs to the north and follow the corridor around to the east and south. Pressing the Switch in the room with 2 Revenants lifts up the bridge to the Blue Key.
Shoot the barrels from here to kill as many enemies as possible. Watch out for the Arch Vile wandering around inside.
When you run across the bridge to grab the Blue Key Demons will start teleporting onto the walkway around you. Drop down to the Radiation Suit in the slime below and take them out from a safe distance.
Make your way back to the computer room where you found the yellow key. Press on the computer in the south-west corner and then on the central computer. This lowers down the lift to the north so you can get out to the yard and also lowers down the pillar with the Soul Sphere. This is Secret 2 but you’ll have to be quick or the pillar will raise again.
Make sure you explore the pond in this yard to find 2 Backpacks and other loot.
Head back to the entrance to the building and walk halfway up the stairs. Climb onto the ledge and from there drop down into the pool of water. Press on the two pillars around the Blue Armor to lower it down.
Head up the stairs and open the Blue Door to the north. Clear out the enemies and head up the stairs to find the Red Key and an Invulnerability sphere.
When you grab it enemies will start teleporting to the center of the room, including an Arch Vile. Now would be a good time for the BFG.
Once you have the Red Key a passage opens up leading to Secret 3. Follow the passage along to Secret 4 and then out into the yard where you can find a Rocket launcher. Press the Green Button before exiting. I think this open the locked door on the western side of the map.
Explore the western yard for a BFG, Backpack and other goodies before opening the Red Bars and hitting the Switch for the Exit.