Level 1
The Installation

Level 2
Ogre Citadel

Level 3
Crypt of Decay

Level 4
The Ebon Fortress

Level 5
The Wizard's Manse

Level 6
The Dismal Oubliette

Secret Level
Underearth

The Crypt of Decay is another relatively linear level. You have to do a great deal of backtracking, however, returning to previously sealed areas after they have been opened. This level will introduce you to a new monster, the death knight. With devastating fireballs and a mighty sword, this towering paladin of doom is pretty lethal - both at close range and at a distance. The super nailgun is a particularly effective means of keeping him at bay. The entrance to this episode's secret level, Underearth, is also located on this level.

The maze of underwater doorways lake will lead you to this red suit of armor

Hurl a few grenades at these zombies to open a passageway to their roost

If you're having trouble getting a 100-percent kill ratio on this level (which you can check by pressing the TAB key), take a little dip before you exit. The numerous fish in the water will apply toward your kill count.

Secret Area 1
From the opening bridge, jump into the water. Go through the tunnel located under the bridge, and follow the arrows. Take the first right and you'll come upon a set of steps that lead to red armor and a teleporter. The teleporter will take you to the sealed door near the first "T" intersection.

Secret Area 2
Near the gold door, at the second "T" intersection, you'll see a ledge with two zombies. Aim your grenade launcher into the air and hurl some explosives their way. The blast will not only take out the zombies, but it will open a corridor leading to their roost, where you’ll find some rockets.

After you grab the gold key, you'll have to face these bad boys

This room houses a shambler, but it also has this button mounted on the ceiling. Shooting it will help you find the secret level

The Gold Key
The gold key room can be found by taking the right passage from the second "T" intersection. Taking the gold key triggers a trap, and the panels on the walls of the room will open. Several death knights will step from the shadows and quickly get to work on your puny frame. To minimize damage, grab the key and run backwards, giving yourself a bit of a time advantage over the knights.

Secret Area 3
After defeating the knights, walk back into the gold key room and enter the alcove on the right. Hit the wall to open a door, leading to 100 health kits and, if you explore underwater, yellow armor. Note the underwater barrier, as it will be mentioned later.

Secret Area 4
After you fight the shambler near the exit, walk into the room full of boxes. Look up and shoot the button on the ceiling. Jump up onto the boxes to the open passage, take the 100 health kit, and push the button. You'll receive the message "The Underwater Barrier is Lowered." This will allow you to access the secret level. You can go there directly from Secret Area 3, but there is a much more interesting method.

"The Dopefish lives!"

Secret Level/Easter Egg
Go to the bridge leading to the exit, just after the hall of nails. You'll notice a thin ledge running along the perimeter of the castle. One side contains rockets, the other a Quad Damage. Jump and grab the rockets, then jump back to the bridge. Jump from the bridge to the side with the Quad Damage. Walk along the thin path, and you'll come to a corridor with some health kits. Drop down into the water, where you'll receive the message "Welcome to the Well of Wishes." This area contains a variety of goodies, as well as a bizarre portrait and the message "The Dopefish Lives." Swim to the niche to the left of the portrait, where the wall will open and you can access the Slipgate to the secret level.