E3M5: The Ophidian Lair (Heretic)

E3M5: The Ophidian Lair is the fifth level in The Dome of D'Sparil episode of Heretic.

Secrets

 * 1) While searching for the yellow key, you will come to a hallway with eight fire braziers. The two westernmost pillars have switches which can be seen in a screenshot below. Press the southern one to open a door on the southern wall of the hallway. Beyond the door, there is the Hellstaff and a varying amount of ammunition for it.
 * 2) Press the northern switch to open a door on the northern wall. Enter the new area to find a Torch along with some health and ammunition items.
 * 3) Collect the yellow key, and three doors will open around you. Every time you cross their doorways, the glass painting on the opposite side of the hallway will open temporarily. Behind, there is a teleporter leading to the barred area northeast of the center room. While the place holds a plethora of valuable items such as an Enchanted Shield, a Ring of Invincibility, a Tome of Power, the Phoenix Rod and ammunition items, there are a lot of strong enemies as well. The first non-boss maulotaur guards the area on smite-meister or higher. Use the teleporter on which you landed to escape.
 * 4) As you have gone past the unavailable green key and opened the wooden door, you will come to a long passage. There are five wooden beams under which there are alcoves with banners. When you are at the middle one, face west to notice that the alcove is deeper and has a different banner. Move towards the banner to make its wall rocket open. The stairs behind the wall lead to a room with many timebombs and health and ammunition items. The teleporter at the end will take you to a small chamber with a Shadowsphere. The rootless wall in front is a one-way door to the center room.