E3M4: The Azure Fortress (Heretic)

E3M4: The Azure Fortress is the fourth level in The Dome of D'Sparil episode of Heretic. It contains an entrance to the secret level E3M9: The Aquifer.

The beginning
You will find yourself in an illuminated hall. In front of you, there is a Dragon Claw and a dim room. As you walk through the hall towards the weapon, you will be attacked by disciples from two side rooms that have been taken over by water completely. The rooms have been isolated from the hall by windows so the enemies cannot enter the hall. Considering that it is not obligatory to return to the starting hall, you may ignore the disciples and just enter the dim room in the north. Once you do it, a wall will raise attempting to seal you in (in case you end up to its southern side, you can lower it again from there). Press the switch to activate the room as an elevator. It will take you beneath the hall where the rest of the level takes place.

During your slow descent, a ledge in the north will become available temporarily. A Ring of Invincibility and one or two Quartz Flasks can be picked up there. When the floor is about to reach the bottom, you will be ambushed by a flock of gargoyles from the west. Quell the attack and enter the door the monsters were guarding. It will reveal the hub of the level with both the yellow and the green door. The northern door is unlocked for now and you need to enter it next.

The yellow key
Behind the door, there is an elongated hall populated by gargoyles. Passages surround a water pool that has some arrows and Crystal Vials in it. At the dead end of the pool, there is also an Ethereal Crossbow. When exploring the wall in the east, you will find three doors. The middle one is the exit door that is shut for now; the entire goal of the level is to find the switch that opens it. The two wooden doors around it lead to another hall that has roots in its walls. You will face two types of danger there. The first one is that there are undead warriors in three separate cages. The second one is that there is a window in the south to a spiral staircase you will visit later on. Ophidians may fire you through the window. As the enemies cannot approach your location, you had better leave them alone and just run to the door that is located opposite of the northernmost cage.

The door will take you to a corridor with various types of enemies. Watch out for the nitrogolem that is able to fire you through a fake window in the south. There is a junction of four routes in the north. The metallic structure in the ceiling is a crusher trap that will be activated as soon as you enter under it. You can spare some ammunition there by luring the present monsters to their deaths. With care, proceed west for a hallway with decorative walls. When opening the door at the end, you may already spot the yellow key in a distance. In addition to the golems in the green chamber, you will also need to beware the nitrogolems that, once again, shoot you from behind a fake window. With the key in your possession, backtrack all the way to the hub chamber.

The green key
The yellow key will give you an access to the spiral staircase of which you saw a glimpse earlier. The required green key is located in the center of the spiral, so you have to descend the stairs until you reach it. Watch out for the gargoyle-ophidian opposition. Once you come back from the key pedestal to the yellow door, you will notice that a new section of the staircase has opened. The area is optional (and considered a secret); at the end of it, there is a well-guarded Hellstaff that can be reached more easily if you use the Torch that lies at the window of the cage hall. Make another return to the hub.

The target switch
Beyond the green door, there is a passage with two long cages. You will find out that weredragons are lurking there. It is recommendable that you kill them now when they are stuck in the cages since they will be let loose later, and you need to go past the cages again for the exit door (unless, of course, you use a Chaos Device or find another exit). At the western end of the passage, you will find a water area similar to those you saw at the beginning of the level. Make sure to avoid the attacks of the iron liches; they cannot enter the passage but they can move next to the window to get a better aim. North of the area, there is an optional hallway that leads back to the green chamber where you found the yellow key. Once you have reached the end of the hallway, you will release a bunch of sabreclaws but also a few goodies, among them a Map Scroll.

However, south of the green door passage, there is a corridor you must yet visit. At the very end of it, you will see a Phoenix Rod. As you approach the weapon, watch out for the weredragons that can fire you from their hideouts. When you possess the rod, a door will have opened about halfway the corridor, north of it. Enter the door to find the switch you have been searching. At the moment, you have two choices. You can either return to the water pool hall to exit via the regular way or you can choose the secret exit that will have opened nearby. Whichever choice you make, you may still want to visit the weredragon cages. They are accessible now and store an Enchanted Shield and a Mystic Urn.

Secrets

 * 1) When you step onto the teleporter in the hub chamber, you will return to the starting hall. The windows have been lowered to provide a route between the hall and the water rooms. Dodge or kill the disciples if you have not done so yet. Enter the western area to reach some Crystal Vials and the Wings of Wrath.
 * 2) Enter the eastern zone to get more Crystal Vials and a Tome of Power.
 * 3) The glass painting in the elongated hall will open when you either step onto or from the stairs in the pool. Behind the painting, there is a chamber with a Quartz Flask and a Shadowsphere as well as an ophidian. You can reopen the door from the chamber.
 * 4) As you open the south-eastern door of the root-walled cage hall, you will come to a staircase. When you spot two decoration torches, press the wall between them. You will find a small room that has a Flame Orb and health pickups depending on the skill level. In addition, you may continue the staircase to its top to surprise the nitrogolem there.
 * 5) In the hallway with decorative walls, stop by the pair of green block walls just in front of the wooden door. You can see a symbol on the southern wall. Press it to reveal a room that connects to the yellow key chamber with a fake window. Kill the lurking nitrogolems in the secret. The window also makes it safe to slay the golems in the key chamber. When you yet go to the eastern end of the secret room, you will obtain another Tome of Power.
 * 6) After picking up the green key, another part of the spiral staircase will become accessible. At the end of the new section, there is a Chaos Device as well as a Hellstaff on its own pedestal.
 * 7) By the pedestal, there is a skeleton wall. Press it to gain access to a small place that contains several timebombs and some sabreclaws.
 * 8) At the moment you open the previous skeleton wall, another door will open in a distance revealing more sabreclaws, a few health pickups and a teleporter.
 * 9) Enter the teleporter to reach a new area with an Enchanted Shield.
 * 10) Step onto the teleporter in the previous secret area to discover yet a new room. Pick up the Morph Ovum and press the symbol wall to get back to the south-western corner of the elongated pool hall.
 * 11) When you have picked up the Phoenix Rod, you can enter the northern weredragon hideout via a secret door. It is located between the two northernmost decorative torches. The chamber holds a Tome of Power on the two easiest skill levels and some minor pickups on the harder difficulty levels.
 * 12) Symmetrically with the previous case, the southern hideout can also be entered. It has a Bag of Holding on the three easiest skill levels and a couple of minor pickups on the hardest ones.
 * 13) Secret exit: When you have hit the switch to open the exit door, return to the place where you found the Phoenix Rod. A door will have opened there. A passage will take you to a hidden teleporter.