Right after the chapter begins, a fight will happen. After you kill all the enemies, go upstairs to the temple. On top of the stairs, next to a corpse, you'll be able to pick up a treasure map of this area.
Get inside and you'll see some swinging blades that you already know. Get through them.
You'll see two moving stones. Throw a dynamite at each of them to unlock the way. You'll find dynamite between the blades. When you do this, go back outside and walk on the left over the entrance. Watch out, mercenaries will attack you once again.
Go where the fire was burning earlier and defeat the first tree zombie in this area. Go along the way, then take the stairs and kill more mercenaries. You'll see the first puzzle here. Turn left by the next stairs and take a big skull from the shack. There will be a smaller one next to it, put it in its place. Head to the entrance and put the big skull into the door.
Now you have to turn its back towards you. Then turn the lower skulls (with burning eyes) as it's shown on the door. The door will open.
Go forward, a few mummies will show up on your way. Then move straight through the corridor, you'll get to a place where you can distribute skill points. Keep going and the ground will start shaking. You'll reach something like a bridge on which parts of the floor fall down. Try not to fall down, it shouldn't be a problem if you're not charging.
At the end there's a boss fight - a full version of the guardian that you've met before. First, shoot him a few times until he disappears. Then a lot of ghouls will appear. My advice: go left as far as you can, to an ammo crate. Remember to have a machine gun. Now turn around and shoot anything that comes to you, you can also use fire from the skulls that you can activate from here.
Finally they will stop appearing, go to the center and upstairs. You'll see some weird machinery. You have to stop it, to do it you just need to stand behind the columns with blue eyes and light them up. Of course, it won't be easy because that bastard guardian will appear again and he'll send more of his minions. Remember to kill them and then light up.
When you do it, the machine will fall apart, and the storyline will go forward. You'll be able to finally get rid of the guardian.
His strategy is simple, he charges at you and attacks. You have to light him up all the time and shoot him, preferably with a machine gun. If you're low on ammo, it should be on the right. If you hurt him severely, he'll disappear and some of his minions will show up. Defeat them and the guardian will appear again. Repeat this until you kill him, when you do it, the chapter will end.