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 most challenging level of Episode 2, Underearth gives you a little taste of what the next two episodes will have in store: limited ammo, minimal health, and a whole lot of monsters. There are also quite a few environmental traps which can be deadlier than a room full of shamblers. One of the best techniques for dealing with these traps - which consist primarily of shooting spikes - is to jump around when the metal is flying. You may feel foolish, but you'll minimize your damage.

The brick sticking out next to the Gold Door will lower the barrier to the Quad Damage

Unless you're desperately in need of some ammo and health, don't enter the building just yet. It leads to the exit and, considering you're without the key, you won’t be able to do anything except fight monsters and gather items. Instead, jump into the water and head through the underground tunnel.

Secret Level 1
When you emerge from the water, you’ll be in a large room. After disposing of the resident guards, look to the left of the gold door, where you'll see a brick sticking slightly out of the wall. Press this brick to open a small area containing a Quad Damage.

Through this alcove is a biosuit which will allow you to find the submerged armor in this room

Using this Quad Damage to take out the monsters in the room is helpful, but it is not the best use of its power. Wait until you've cleared the room, then take the Quad and quickly move to the stairway leading out of the room. You're about to face an army of zombies, and Quad Damage is an incredibly effective tool against these undead pests. The extra damage enables you to destroy them with shotgun blasts instead of rockets. Since a roomful of zombies can deplete your rocket supply in no time, a lighter weapon is a good way to economize ammo - especially considering the relative abundance of shells throughout the game.

Secret Level 2
In the room just beyond the gold door, drop into the toxic slime. Quickly walk into the visible alcove, grab the biosuit, then move under the walkway. Almost directly below the center, you'll begin to sink. Follow the submerged tunnel to the red armor. To exit the pool, press the star button next to the alcove, which will release a small set of steps.

There's nothing in this secret room but the symbol on the wall and those mysterious initials

In the nail trap room, notice the clockwise sequence of the firing. If you jump and run with the firing, it is possible to avoid taking very much damage. Before opening the door, you can jump onto the turret to attack the ogre. He won't so much as scratch you, and you can lob a few grenades at him through the doorway.

Egg
Throughout this level, you'll see several pictures of gargoyles. If you hit or shoot the pictures, you'll notice that they bleed. Hit every one on the level - there are seven - then walk into the long flashing corridor just before the exit. Walk into the second dark niche and hit the wall. You’ll find a strange room with a large red emblem on one wall and the initials "T.C." and "T.W." carved below it.