Cross the bridge and engage the three ogres you meet in combat. Continue up the stairs and you'll arrive at a large room, guarded by scrags and death knights. Kill them then attempt to open the doors at the opposite end, you'll be told to go for a swim. Return to the bridge and drop into the water to the left as you walk away from the building. Look for a hole in the wall and swim through to another room. Deal with the ogres you meet, and then a fiend will also attack. When the room is clear, shoot the two faces that are each side of the first doorway, as shooting them throughout the level will allow you access to a secret room later. Look at the quad damage, there is a brick to the right of it, if you press it, you can get the quad and a secret. You may like to leave it here, until a little later. Go through the far door and drop some grenades down the stairs on the zombies. Continue to a large area with several zombies and an ogre up on a ledge to the left. Duck in and out of the doorway avoiding the ogres grenades and dispatch the zombies. Kill the ogre on the ledge, then step on the ground switch which starts a huge spike crushing down, killing the fiend, and opens the cage. Enter it, avoiding the spike, and collect some armour.
Get the quad damage if you haven't already used it. Run back down the tunnel, and beyond, and be prepaired for ogres, scrags, death knights and fiends. Follow the walkway around and grab the 100 health bonus. Two fiends will be released, kill them and shot at the face on the wall. Run toward the passage on the left, and kill another fiend, The next room contains nail traps in the wall, an ogre dropping shells from above and death knights. The nail traps are activated by stepping on the blue area on the floor. Get in the lift, and kill the ogre on the platform opposite. Follow the corridor and grab the gold key and enter the gold-key door ahead. Kill the scrags and the ogre, then make your way to where he was just standing. Look for a button on the wall in the slime, and a gap. Jump into the slime, and head through into another room, grab the bio-suit and the box of nails, if you're feeling lucky, head diagonally to the left corner near the other button and wade around until you begin to sink. Swim down and grab the Red armour. Immediately head back to the other button, press it and jump up the stairs. Press the other switch and then go through the doorway it opens, Kill the ogre and shoot another face in the wall. You'll soon encounter some more scrags. Turn left into some more ogres, death knights and scrags. Shoot yet another face and go over the bridge. You may encounter more death knights, if they didn't come out earlier, don't tackle them in the room ahead as it's rigged with nail traps in the walls. When they are dealt with. You need to hit all the buttons in the room. Now go through the room ahead. Kill the ogre and shoot both of the faces on walls. Run through the hall and kill the fiend. A death knight waits to the immediate left, and another down to the right. If you shot all the gargoyle heads up until now, you can shoot the back wall of this second nook to reveal a room with a quad damage rune. Proceed down the hall and press the wall button at the end of the room to several zombies, and two more buttons. Hit all the buttons and proceed tp the stairs and through the now unbarred door to the next level.