Start by heading towards the main building, grab the pentagram of protection. Step off the walkway into the lava, make sure you stay near the platform, turn around and swim through the gap into a secret area with some health and the quad damage. Step through the portal and now head back to where you started, and get in the lift. Kill the ogres you encounter. Get the rocket launcher in a room to the left, return to the corridor and blast the ogre at the end. Turn where you see the entrance with the crosses. Jump up on to the ledge above. Waste all the ogres and scrags, get the mega-health and press the quake symbol on the wall.
Return to the pyramid where you got the pentagram. Enter the pyramid and continue forward. You meet two orges oin the room beyond, one on the ledge above to your right. Kill them and hit the button on the ledge. Turn around and head for the new lift in the left hand corner of the main room.
Ride it up to the sliver-key door, then turn left, and battle more ogres. Make your way to the landing above the lift and grab the yellow armour. You now have to take on some ogres, scrags and a shambler on a central platform.
After defeating them, press the button the shambler was guarding. Turn around and go to the edge of the platform. Drop down to the nearest ledge, battle more ogres, get the silver key from the pedestal, and fight yet more ogres and scrags. Head to the silver-key door. Destroy the ogres, but don't got through the portal yet. Walk up the left and look for a block in a wall on the right hand side of the left passage. Shoot it for the second secret. Now you can exit.