This level has an especially interesting layout and design, with a lot of well-built bonus areas. You begin outside on top of a construct, near the level of the sky. A wide stairway leads down to a door. It's all surrounded by a railing too high to jump or even see that well over, but you can see that the construct is in the middle of a big area of unknown depth, with wooden columns here and there. Fire off a shot or two, and you'll attract a bunch of Gargoyles. After fighting them off, open the door and go inside.
Inside is a wide, tall, elaborate and very long hall. On the east side, to your right, is a Yellow Door, followed by a side route leading to a doorway out of reach above, followed by another Yellow Door. On the west side, to your left, is a long, tall corridor leading up, followed by a long window looking into a big, deep water-filled room crammed with floating spores, followed by a second corridor leading up, similar to the first. At the far, north, end is the Blue Door.
Go up either route on the west side of the main hall. They both lead up to either end of a long tall upper hall; you'll notice this hall, as well as the main hall, have a symmetry from end to end. This symmetry exists throughout most of the level. In here are several cages containing enemies. At either end of the hall are hidden cages covered by one-way windows; you may be fired on by Undead Warriors inside. There are bonus areas available here. Look for the inset part of the wall, between the one-way-window cage and the lava-filled cage nearby. (They're behind the floating spores.) Shoot at the back of the inset area and a hidden door will open, leading to the one-way-window cage. Additional routes within these areas will be open later.
Look for two switches near the middle of the hall, on the long side opposite the corridors that led up here. Hit the switch on your left: it opens a small room nearby, at the center of the long side. Shoot at the back wall (with the red eyes) and it will open, with a tall side room beyond. After fighting the enemies, hit the right-hand switch, then go back inside: two side areas have opened, with some enemies plus items including a Ring of Invincibility, and a switch has been uncovered. Hit the switch, then go back out to the upper hall and continue walking straight ahead to the far side (between the wooden cages, where the Dragon Claw is/was) and you'll see the wall slowly lowering like a lift, revealing an opening into the big watery room below.
Before jumping down, a couple bonus areas are now open. Go to the one-way-window cages at the ends of the upper hall whose doors you shot open earlier. In each, another passage opened when you stepped up to the switch that opened the watery room. Follow the long stairway up, drop down to an item, and drop down again back to the upper hall.
In the watery room, it's possible, although hazardous, to set off the spores and get them to take out the Gargoyles and Golems clogging the area. Shove your way past the spores and enemies, or run over them if you're on the lowering lift and it's still high enough, to the stairs leading down to the water. After setting off the spores, stay at the center of the room, which is near the bottom of the stairs, until they finish chain-reacting. You may try using the Ring of Invincibility you picked up recently. When you step onto the water, compartments at either end of the room will open, releasing Disciples of D'Sparil. If you time it right, you can get them with the spores as well, although it's difficult.
In front of the window looking into the main hall, you'll see the Yellow Key barricaded by bars. You'll notice the wall/lift that you entered the room on stays lowered. Go and step onto the lowered lift, then look on either side in the watery room, and you'll see wide lifts leading up to the wooden cages have momentarily lowered. Look for and hit the switch inside one cage, and it opens the bars around the Yellow Key. Collect it, then activate the section of wall with the grating at the bottom on either side of the window. Both sections are doors leading back to the main hall.
North Yellow Door
Go to and open the northernmost Yellow Door: the one closest to the Blue Door. A bit to the left, a long corridor leads down, where you'll find the Green Door, and Undead Warriors shooting at you through windows. Note that inverted pillar hanging from the ceiling (with the red tapestry). Step under it, and the windows convert into doorways. When you step into the room inside, the back wall opens, with a few more enemies.
Back up the corridor, opposite the Yellow Door, activate the section of wall with the red tapestry, and a door here opens. Hit the switch inside. When you opened the door, a side area nearby also opened, with a minor ambush. There are a few items there.
Go back to the main hall, and look for a nook in the wall just inside the door you first entered the hall from, that wasn't there before. It'll be to your right just before you exit. Hit the switch inside: this raises stairs to the out-of-reach doorway on the east side of the main hall.
South Yellow Door
Before going upstairs, take a look inside the southern Yellow Door. Nothing in here is critical, but there's a bonus area available. In here is another long corridor leading down, at the end of which is a second Green Door. Opposite this Green Door, activate the wall with the red tapestry to open a door. A stairway leads steeply down to a large landing, switches back to your left and continues down into darkness. Step down the dark section but then turn around and go back to the landing. The back wall here opened, releasing enemies. After fighting them, go down the dark stairs, where you'll find a smallish dark room containing a Hellstaff. The back wall will open when you step forward, brightly lit behind, with some enemies.
Go now to the stairs you raised near the midpoint of the main hall. Up here is a big hall with many regularly-spaced columns, four doors along the opposite side, stained-glass windows at one end with an out-of-reach platform in front of them, and several alcoves out of reach containing a lot of items. If you go for the items in the corners, the overhangs above will become crushers, so step away quickly. Through the four doors is a long balcony overlooking a huge outdoor area. The railing is too high to get over and also limits how much you can see, but you might still be able to clear out a few enemies.
Back inside, you'll see the Green Key in front of the center stained-glass window. Examine the center row of the three rows of columns spanning the length of the room. You'll find switches on three of them. Hit the switch that's farthest from the windows, then run to the windows: the switch momentarily lowered the platform. Step onto the platform and then back away: the windows are one-way, and doors behind them have opened, releasing an Iron Lich and several Disciples of D'Sparil. After fighting them, activate the platform again and collect the Green Key.
This was your only necessary task in here, but this part of the level is absolutely replete with bonus areas. Take a look behind the windows. The center one has armor; the others nothing--for now. Go to the three switches on the columns, hit the center switch, then go back up to the windows. Additional doors have opened behind the left and right ones, leading to a back room with two teleporters. Each goes to a low-ceilinged labyrinth. Find and hit the switch, and the walls making up the labyrinth will lower, converting the area into a single room and releasing a few enemies. Activate any walls made of dark-metal texture you come across: these are doors and in one instance a lift. Follow all the passages you find. They lead to low alcoves up on the walls in many areas, including the areas past the Yellow Doors, the stairs leading to the many-columns hall, and the ones in the many-columns hall itself. You probably saw some or all of these earlier. Items include a Map Scroll, a Mystic Urn, and this level's Time Bombs of the Ancients cache. If you're after a full kills tally, when you get to the two small alcoves along the side of the many-columns hall, jump out and down into the hall. In each case, two of the columns will lower, releasing a couple Disciples of D'Sparil, for a total of four. You can ride the columns back up: if you do, the switch in the compartment above lowers the columns again. (The switches don't do anything else.)
There's one more hidden area: note the column in the center row that's farthest from the windows. Go hit the switch closest to the windows (the one covered with spiderwebs), then return to the farthest column right away. A lift in the floor next to the column has lowered, revealing a teleporter under the column. This goes out to the outdoor area where you began the level, only you'll be on a ledge around the perimeter of the overall area, and you'll see it's fairly deep and water-filled. Follow the ledge to either end. Long side areas will open, releasing enemies. There are items including Greater Runes and an Inferno Orb. Down in the water there are many more items. The teleporter in the water returns you to the ledge. To exit the area, follow the ledge to either end and make a running jump down to the railing outside the door to the main hall, where the torch and Quartz Flask is (don't forget the Quartz Flask on the other railing).
Go to and enter either Green Door. They lead out to the big outdoor area with the balcony outside the many-columns hall. You'll see it's very deep and water-filled, and get a look at the elaborate series of terraces opposite the balcony, swarming with Golems. Get all the enemies cleared out, then look for and follow the narrow passage in front of the first terrace. You'll come to switches that activate lifts leading up. Before stepping off the lift, look up at the balcony and the four doors. In between the centermost ones is a big compartment containing a huge horde of Disciples of D'Sparil. It will open when you step onto the terrace from the lift. You might try running up the stairs to the second terrace and fire your Phoenix Rod toward the compartment before the Disciples have had a chance to spread out. After fighting them, go up the stairs to the second terrace, and activate the wall with the gold symbol to lower a lift to the third terrace. Activate the inset wall with the gold symbol to open a door to a small area with a switch. Hit it, and stairs leading up to that platform next to the balcony will form. On the platform is the Blue Key. When you step onto the platform, an area to your right will open, containing a single Iron Lich. The switch inside momentarily lowers the railing around the balcony, allowing you to get to the balcony from down at the water as well as allowing access to the Phoenix Rod and ammo on the railing. Look inside the Disciple-of-D'Sparil compartment, and you'll find Wings of Wrath. (The railing actually lowered a bit when the Disciple-of-D'Sparil compartment opened, so if you had returned to the balcony you could have gotten to the items then.)
Inside the Blue Door is the level exit. Step inside the room, but then go back to the upper hall and to the one-way-window cages you shot the doors open to earlier. In each, a second route opened when you stepped into the exit room. These new routes go to the lava cages nearby, where you'll find another Ring of Invincibility and Mystic Urn.