Look over the ledge, and kill the ogre below, then drop down and step on the floor switch. This opens a door down the hall to your left. Enter the hallway and shoot two more ogres. Go through the doorway ahead, and turn right, you will see a button you to press and a rocket launcher. Pressing the button opens a door down the hall. Go through this to get the yellow armour. Press the button you find there to open a pit behind you. It also reveals a pair of angry ogres on the ledge to the right. Kill them, as they guard a 100 health bonus you can get later. Drop into the nearby hole. Kill the two ogres past the lava that guard the silver key, and descend the stairs. Make a right and run for the 100 health bonus at the end of the hallway. You need to kill the ogre that's released for a lift to relative safety to be unbarred. Get on the lift and get the silver key. Jump back over the lava to the sunken stairs. Wait for the door with the spikes to pass, turn left and go through the portal to the next secret. Kill the scrags and grab the nails. Look down and find the 100 health bonus from earlier. You should be able to get to the ledge with a jump. Retrace your steps back to the floor button at the beginning of the level. Turn right, go through the darkened doorway, in the shadows is a pit with a contorted beam stretching over it, if you fall off, nail traps will get you. An easy way across is run over the first straight part of the beam then jump. You should land safely on the other side, where you'll run into several ogres. Continue on and kill the ogre and zombies. Hit the button on the far wall beyond the pillar. Three new zombies that drop from the ceiling, kill them, and head over the bridge that rises out of the lava. Enter the silver door and step on the floor button. That extends a platform to the golden key, and a portal. Stand before the pillar with the portal to your left and shoot the red symbol. Now turn left and run for where the stairs to the portal were. Enter to find another secret, wait for the stairs to rebuild and enter the next portal for another secret area. Grab the 100 health bonus and drop down, enter the portal up the stairs.
You are now on the ledge were you started. Drop down and kill the ogre hiding by the lift. Walk over the plank and grab the gold key, turn and be prepared for fiend that will attack you when you reach the alcove. It should drop into the lava. Run straight off the plank into the far room. Look at the concealed door at the far right side of the room. Approach it, stand with it to your right side, look up and shoot the red Quake switch up on the wall, The door opens, get on the lift. Once you're up at the top, go forward a little and spot a ledge just below to the left. Drop to the ledge and grab the quad damage. Drop off to the floor and head back to the main room, open the gold-key door. Kill the two ogres and press the button on the left wall. This opens another door at the other end of this hall. Rush through the door and step on the floor button, kill the shambler while you still have the quad power.