Level 2
Castle of the Damned

Level 3
The Necropolis

Level 4
The Grisly Grotto

Level 5
Gloom Keep

Level 6
The Door to Chthon

Level 7
The House of Chthon

Secret Level
Ziggurat Vertigo

The heat is on! In Level 4 you have plenty to worry about in addition to the ever-present enemies. While you can swim in some pools but not in others, finding two of the three secrets depends largely on how long you can hold your breath. Also: At the very end of Level 4 is a hidden portal that takes you to this episode's secret level!

Secret Area 1
Shortly after you start Level 4, the door in front of you pops open and a scrag attacks. Slay him and step through the door. You can hear the grunts of knights from below. Shoot the two sun symbols, and the ceiling will drop down and present you with a new suit of armor. Pick up whatever power-ups you need, then head outside.

Shoot the pair of sun symbols to get new armor

If you immediately shoot the symbols, there's an above-average chance that the ceiling will crush the knights.

The biosuit it isn't really necessary for exploring the lake. Just be sure to surface periodically.

There are two exits from the lake, and both are easy to find. The first, a small green cove to the right, leads to a locked door, which is opened with the silver key. Use your double-barreled shotgun to eliminate the knight squad, grab some health kits and ammo, and return to the lake. The second exit is in the maze of corridors found at the bottom of the lake.

You can quickly change your swimming depth by pressing the Z and A keys. Surface where you see the red up-arrows.

You're now inside a small castle. The objective here is to reach the exit and retrieve the silver key that's suspended over the dock. It's a short trip, but one that's filled with enemies - ogres, scrags, and knights. After getting the key, return to the green cove and enter the second castle.

Secret Area 2
When leaving the dock, look to your right. You'll see a black patch of wall. A short way down is a small entrance that leads to a case of rockets.

This room can be a death trap. Run to the elevator platform at the end!

Use the silver key to enter the second castle. In the first hallway, step on the emblem in the floor to open a secret panel that reveals another suit of armor.

The five floor triggers release flying spikes. You must trigger each one by stepping on it. The sequence doesn't matter. When you're done, two new panels open on the side walls, leading to the ogres that were previously attacking you. Drop through one of the openings, and destroy the ogres. Shoot the other ogres on the opposite platform. When you jump down (there's no other way to leave the platform), aim for the walkway in the center. Take the elevator back up, and claim the prizes on the other platform. Jump down to the walkway again, and take the elevator back up. To finish the level, climb the stairway on the left wall and fight your way to the end.

Secret level! This teleporter beams you to a secret place.

Secret Area 3
You'll see a wall-mounted emblem on each of the two small platforms. After pushing both emblems, a message appears that states: "A Secret Cave Has Opened." Locate this mystery cave and you've found Quake's secret level!

Secret Level
Go back to the lake. Just to the left of the dock (the dark area), you'll find a new opening. Inside are several power-ups and the teleporter that leads to the secret level, Ziggurat Vertigo.