E4M3: Ambulatory (Heretic)

E4M3: Ambulatory is the third level in The Ossuary episode of Heretic Shadow of the Serpent Riders.

Walkthrough
You start at the southwest corner of a metallic hall, with doorways leading out on both the northern and southern side. Although your first objective is located to the south, the northern side holds an Ethereal Crossbow, so you may want to visit there.

Crusher trap and yellow key
A large square-shaped zone in the middle of the hall is brighter than the surrounding edges. The bright zone actually consists of 36 (6 x 6) individual sections, many of which have a trap set. When you step onto a section, its ceiling will start to operate as a fast crusher. The behavior applies to 21 cases. However, the remaining fifteen sections in the grid form a contiguous route from an edge to another and have static ceilings. You are able to spot the way with the help of two clues:


 * The series of timebombs works as a guide. When you collect the artifacts by always taking the one nearest to your location, you can cross the zone safely.
 * The section with the first timebomb has a unique ceiling flat. When you step onto it, the lighting of the next section in the series will be darkened. By stepping onto the darkened sections, you will not activate any crushers and will eventually reach the northern side. Have a look at a screenshot of the place for a demonstration.

Enter the doorway to a wooden corridor that has the crossbow and each locked door. Return to the southern side of the metallic hall and leave the area. A few steps away, there is a passage that actually is a part of an octagonal circle. In the beginning, its other sides are inaccessible, but the more you make progress, the more of it will be revealed.

Proceed to the opening in the passage to see a great outdoor crater with the yellow key in its center. To reach the platform on which the key spins, simply move forward, and you will find out to be on a rising bridge. It will work as the route between the key and the opening you came from. Notice that if you fall into the lava, you can only survive by using the Wings of Wrath or a Chaos Device. The progress is as follows: each locked door at the north conceals a room with a switch. When you press one, a new bridge will rise at the crater giving you an access to an unexplored area. Now that you have the yellow key, go to unlock the relevant door and press the switch. It will raise the western bridge.

Green key - western section
After crossing the bridge westbound, you will first arrive at an identical part of the circle. Further away, there is an indoor area with a pool of sludge to the north. On the bottom, there is an aggregate of pods, while in the middle, there is the green key on an unreachable platform. It is important to know that you may not drop yourself into the pool at the point of the level, since there is no way to escape. What you need to do, instead, is to open the wooden door and examine the storeroom beyond. When you press the switch there, the green key will come down, and it becomes safer to enter the sludge pool.

The northwest and northeast corners of the pool have ladder-like stairs that both lead to a disciple's chamber. The place beyond the former corner holds a Morph Ovum while the other has a Shadowsphere. When you grab the key in the center, an elevator at the northern end of the pool will descend, allowing you to exit. Once you have traveled up, you will be confronted by three iron liches. However, passages begin to both your left and right, and you can use either one to flee if it is necessary. The passages lead back to the southern ledge of the sludge pool.

When you return towards the crater, you can notice that the northwestern side of the octagonal circle has been opened. Outside the circle, there is an orthogonal room made of stone. The area at the end contains a Bag of Holding. Proceed to the metallic hall and press the switch behind the green door to raise the eastern bridge.

Blue key - eastern section
Once you have passed the portion of the circle, you will come to a fork where there are two downward staircases. They both lead to a big flooded cavern with moss-covered walls. Solid wooden pillars are scattered all over the area, but the easternmost one is broken midway and has the blue key in the gap. As you walk northbound from the key, you can see a doorway leading out from the cavern. By stepping in, you will make six windows in the cavern walls go down and allow nitrogolems to enter the area.

Behind the windows, there is an unbroken corridor that circles around the water cavern. The southern end has a Hellstaff while the opposite end holds a Torch. You need to trigger three actions in the corridor in order to proceed:
 * 1) In the proximity of the blue key, there is a switch. Pressing it makes a Tome of Power available at the northern end.
 * 2) When you are about to collect the artifact, a wall with two eagle insignias will open nearby.
 * 3) As you finally press the switch at the end of the freshly accessed area, the key will come down.

Have the key and return to the border of the crater area. The northeastern side of the octagonal circle can be accessed now. A few golems have become freed in another orthogonal room. Make your last visit to the key doors and press the third switch to raise the remaining bridge.

Exit - southern section
Go to the circular green hall. Although there is a Phoenix Rod in its center, do not take the weapon but return to the octagonal circle. The southwestern and southeastern sides of it have finally descended, rendering the circle complete. On the sides, there are yet two more orthogonal areas. The southwestern one hides the Wings of Wrath and two Quartz Flasks.

When you grab the Phoenix Rod, three doors will open uncovering new areas. The room to the east is a small one and has two disciples. However, the opposite room is not only bigger but also has a mightier opposition: in addition to the numerous disciples, there is a maulotaur that is able to harm you from behind a window. Your last effort is to press a switch in both rooms. The switches are located in alcoves and will raise the bars in front of the exit door, hidden as well until you took the rod. Enter the aforementioned door and walk onto the exit teleporter.

Official

 * 1) In the metallic hall, the section with the fourteenth timebomb is special: instead of becoming darkened, its lighting will start to blink as a signal. It is not a design error but an indication that the adjacent wall is a secret door. Enter it to reach a long passage with a room at its end. (sector 146) There is a Tome of Power and a window to a chamber with three iron liches. The monsters are a potential threat when you get the green key later in the map. If you are armed properly, you can destroy them already.
 * 2) By entering the aforesaid chamber subsequently, you will open two secret passages back in the storeroom. The passages lead to a room that, in turn, leads to a staircase. When you go upstairs (sector 170), you will meet a maulotaur that, if left alone, is a danger to you later in the southern section of the level. As in the previous map, you can lure the monster away from his post and eventually direct him to a place where he becomes less harmful. Utilize the sludge pool in this case. The maulotaur's chamber is a cache for a Map Scroll, a Bag of Holding and an Inferno Orb.
 * 3) The northwestern orthogonal room with the Bag of Holding has an eagle insignia on a wall. Press it to reveal more of similar architecture. The uncovered place contains some Mace Spheres and an Energy Orb. (sector 142)

Non-official

 * 1) The northern wall opposite the Tome of Power in the blue key area has its texture misaligned. Press it to reveal a passage with two staircases: a short one and a long one. Once you have reached the top of the former, the floor will drop. Beware the fire gargoyles that can fire at you through a false wall from the south. When you have passed the long staircase, the passage will bend to the left and end near a unit of Ethereal Arrows. If you press the western wall at the end, you will yet open a shortcut to the metallic hall.
 * 2) The northeastern orthogonal room has a wall with an eagle insignia, just like in the case of secret 3. Press it to find a hidden area. One end has a Chaos Device while the other has a new insignia.
 * 3) Yet hit the aforementioned emblem to reveal a room. It is the place where the fire gargoyles could attack you. There is a Ring of Invincibility.
 * 4) The southeastern orthogonal room uses a more advanced version of the secret door. When you press the local eagle insignia, the wall will open but the structure behind you will also descend. An Enchanted Shield and four Flame Orbs will become available. The area beyond the insignia contains a Mystic Urn, a Quiver of Ethereal Arrows, Greater Runes and another Morph Ovum.
 * 5) Each time you open the exit door, a wall in the eastern green room will open as well. The wall closes after a while but can be reopened from its other side. Proceed to the mossy end of the exposed secret passage. Walk towards the metal wall there, and you will end up activating a door after another. Finally, you will open a passage to the corridor at the blue key area, but during the process, a doorway to the east will become uncovered too. Enter it to find an iron lich in a square room. Eleven serpent torches form an L-shaped wall, with the right angle being at the northwest corner. The monster cannot attack you as long as you stay behind the obstacles. Move to another corner to bypass the wall and destroy the lich. You can find a Pile of Mace Spheres, two Quartz Flasks and a Ring of Invincibility in the area.

Firemace
E4M3 is the first level in the episode where a Firemace can be obtained. In case it has appeared at the level startup, you will find it from one of five different positions. In order of appearance, they are located


 * in the northwestern disciple chamber near the sludge pool.
 * on the bottom of the staircase in secret 2.
 * in the switch room behind the green door.
 * in non-official secret 2.
 * behind the wall of non-official secret 5.

If the weapon did not appear, the next chance to find it is on the following level.

Trivia

 * For an unclear reason, E4M3 does not have any ambient sounds set. E4M4: Sepulcher lacks them as well.