MAP20: Silures (Eternal Doom)

MAP12: Dark Dome is the twentieth level of Eternal Doom and was designed by Bob Evans.

Yellow Key
Getting the yellow key is complicated. Start from the room with the open hallway and the mud on either side (with the candles at the end). Exit this area and take a right, back to the grey rock cave filled with water, where you first came into this area and fought a Hell Knight or two. A hard-to-see narrow stairway on the left leads up into a stone area with a couple of Demons in it. At the end of this room where a couple Demons pop up is a red switch. Hit that switch.

On your way back, you can get a plasma gun. There's two skull switches right near the top of the stairs (one is around the corner). Hit the furthest one and a wooden room will open up near the top of the stairs. Enter that room and fight a Hell Knight. The rear wall opens up onto the grand hallway (with the trees outside). Don't exit yet, instead go back and hit the other switch to lower the window ledge in the grand hallway. Run back through the wooden room before the ledge goes back up, through the automatic door, and straight across before the ledge goes back up to get to the outside treed area. Pick up the plasma gun in the corner.

Go back to the mud hall. There's two teleporters right before you go outside into the mud hall. Go in the one closest to the mud hall, and you will be transported into a water area. On either side is bars and an energy cell pack, and there's a teleporter in the middle. Don't go in this teleporter. Instead, turn around and notice the bulletholes in the rear wall of the teleporter you just came out of. Shoot that wall and a teleporter will open on the other side of the room. Go through that teleporter and you will teleport into the left cage. Go to the end of the cage and activate the demon head wall switch. This opens up another switch in the next room, so you have to be quick. On the left wall is another sort tablet-y switch. Open it to reveal a teleport and jump in.

You will teleport back to that stone room with the Demons in it. If you did it quick enough, there is a skull switch that is right in front of you. Hit that switch and quickly run to the rear of the stone room where a door has temporarily opened up. Head through (gaining a secret area bonus) and collect some rockets. Go through the waterway and vines and you are now in the yellow key room. A small stairway on the side leads up. Head to the rear and watch out for two Revenants. Around the corner is a switch. Hit that and the rear will open up. Head in and fight an Archvile. Once you have killed him, take a look at the statues. On the left side, one of the statues is missing. Activate this wall and a pillar will open up to reveal the final switch. Hit this switch to lower the yellow key and pick it up.

Head back out to the grand hallway (you can use the other teleporter near the mud hall, or use the plasma gun shortcut). Go in the three-eyed skull door (at this point you've been in here already I think). Ahead is a barrel and a disembowled corpse. At the right is the yellow key door. Activate it, and step up on the left hand yellow key marker to get onto it (it doesn't go down all the way, but the marker has a tiny bite taken out of it).

The previous level is MAP19: Warheros (Eternal Doom)

The next level is MAP21: Fire and Stone (Eternal Doom)