Level 28: Heck
Back to Final Doom
From the Start run forwards and grab the Blue Armor. Turn back and take out the 4 Revenants on the pillars. With the room clear you can pick up the Rocket Launcher and Super Shotgun in the center of the room.
This level is composed of three sections to the east, south and west and the Exit to the north. You’ll find one key in each section and I believe you can do them in any order.
Starting with the area to the west clear out the Gunners around these corridors and look out for the Shogun Guys behind the fake walls. This is where you’ll find Secret 1, which is actually 3 secret locations, and Secret 2. See the map above for exact locations.
Explore the corridors to the south and west first and find the Skull Button. When you press it an Arch Vile is released behind you and the corridor to the north will open up.
Explore the corridor to the north until you find the Blue Key. Once you pick it up another Arch Vile will be released behind you. Continue exploring and when you’re ready return to the Start.
Head to the south and take either path to a circular room with an Arch Vile on a pedestal with a Megasphere.
Take it out and then press the Button to lower the pedestal and open the door, releasing 3 Revenants. Use the central pillar to avoid their fireballs.
Press the Button again and go through the door to the south. You’ll come to a rectangular room with Demons and Lost Souls on a red floor and Mancubus on walkways around the edge. Take them all out and then ride the lift up to the walkway on the left. Head around to the back of the room for the Red Key.
Once you pick it up Revenants will be released from the side wall. Once you’ve killed them head up the stairs and make your way back to the center.
Head to the east and take out the Revenants on the ledge to the left. Make your way around to a lowered room but watch out for the Arch Vile and Pain Elementals.
Once the room is clear grab the Yellow Key and use the BFG to kill the Revenants and Mancubus that are revealed from the wall in front of you.
Around the back of this room you’ll find a Megasphere if you need the health. On the way back to the center some more rooms will have opened up with an Arachnotron, Hell Knights and a Baron of Hell. Take them all out and return to the Start.
Now that you have all three keys take the path to the north. Open the Red, Blue and Yellow Doors. Watch out for the group of Lost souls behind the Yellow Door and then drop into the Exit.