This is the only full-sized level of the game without keys. You begin in a large, empty, dimly-lit yard across from a building with two windows and an entrance blocked by bars. To the left of the building you'll see a narrow stone door. This will be open later. Step up to the barred-off entrance and the bars will open, allowing you to enter. They don't open from the inside, but you'll be returning outside by a roundabout way.
Inside the building you'll see what looks like a fat column with panels on every side featuring the exit symbol. As the symbols suggest, the main level exit is inside here, and is opened in two stages. Also in the room are two stone doors, to the west (left), and east (right). Each of these doors leads to one of the two side areas of the level. You can do either one first. When you step up to either door, both doors will momentarily open. Before beginning, step through either door and then return to the central room. Four compartments in here have opened, releasing a huge crowd of ghostly Golems. By taking care of these now, they won't sneak up on you or get in the way later on. In each compartment is an item.
In here, at the end of a corridor, is a round room with a high platform in the center. To the left are windows looking into a doubling-back pathway leading down and away. You should be able to get rid of most of the enemies in there through the windows. (Tip: use your Dragon Claw.) Go to the side of the platform on the far end of the room and activate the section with the large gold symbol. After the platform lowers, step onto it. The central column will open, revealing a smaller column with a switch. Hit this switch, and the exit-symbol panels in the central room will be opened. (The exit portal inside will be covered up by a smaller column if you haven't completed the east side yet.) Although this was your only "official" task in this side, the rest of the side is well worth seeing plus completing it is necessary in order to fully access the level.
West side additional areas
When you stepped up to the switch, a door in the room will have opened (where the large gold symbols were) leading to a short passage with a switch. Hit the switch in here, and a door to your left will open, leading down to the doubling-back pathway past the windows. Go down to the pathway, but then turn around and go back up: a compartment next to the switch has opened, with a few enemies inside. Also, go back to the corridor toward the stone door. Areas on either side have opened here too, with a bunch of enemies and several items inside.
Now that these ambushes are out of the way, go back to and follow the doubling-back pathway down to where it ends in a room with a low platform. First, go around behind the platform on the right, where there are steps to the platform, and collect all the items. Then go around behind on the left side: you'll find a switch that activates a lift leading down. Ride the lift down, and follow the meandering stairway up to where it leads to a small yard. (Watch out for the Iron Lich in here.) When you step into the yard, one of the walls will lower, connecting it to the big yard outside the building. At the opposite end of the yard, a second area has opened, with enemies and items inside. When you step into this second area, the narrow door to the left of the building will open. However, there's another door immediately behind it that you open from the east side.
Inside here is a room with a series of terraces or steps. Go to the highest step: this is a lift that will lower when you step on it. Follow the dark-paneled corridor to a large room that looks like a mausoleum. After clearing out the enemies, step up to the coffin at the far end with the Ethereal Crossbow. The red sections of the walls on either side will open, revealing two side rooms. Take care of the enemies, then go back to the dark-paneled corridor. A nook here has also opened. Hit the switch inside the nook, and a second nook with switch opens next to it. That switch opens a third nook and switch, and that one opens a fourth nook/switch. When you step into the fourth nook, two compartments near the lift will open, with an ambush inside. Get rid of the enemies, then hit the fourth nook's switch. This lowers all of the terraces in the room before the lift, allowing you to return to the central room. The exit portal inside the fat column is now uncovered. (If you haven't been to the west side yet, the exit-symbol panels will still be closed.)
East side additional areas
As with the west side, there's more to see on this side. The switch in the fourth nook also opened doors in each of the side rooms adjacent to the mausoleum. The one in the left-hand side room goes to those two dark cages, where there are items. Watch out for a big ghostly-Undead-Warrior ambush as you're leaving the cages.
Go through the door in the right-hand side room: this is a short passage that goes back out to the yard outside the building. When you return to the yard, yet another side area will have opened, on your right. Step into here, and the inner door to the left of the building will open.
Past the two narrow doors to the left of the building is a compartment with a switch. Hit the switch, then go back inside to the central room. Ignore the exit portal; there are far better things in store. That high ledge at the back of the room will have lowered, revealing a big stairway leading down and outside to the back areas. This overall area is mostly symmetrical, with left and right sides that are mostly the same. At the bottom of the stairs, there are three ways you can go: ahead is a courtyard; to the sides are pools of icky water, beyond which are meandering passages that go to the far end of the courtyard.
First, clear out the enemies in the courtyard, then look at those three columns in the covered area at the far end. On the back of the center one is a switch. Hit this, and a stairway up to the Phoenix Rod and stairways leading up to the side ledges in the courtyard will form. Remember to go up to them, because there are items. Check out the pools: in each is a weapon among the spores. When you pick up the weapon, compartments surrounding the pool will open, with an enemy horde inside. It's possible to take out many of the enemies by setting off the spores after the doors finish opening, although this is fairly difficult because your weapons-fire will usually impact the enemies and not the spores.
Secret Level Alert
This episode's secret level is accessed from this level. That was the real reason for opening up this back area. Along the meandering passage on the east side, there's a false wall covering a hidden area. Carefully follow the inner wall (the one closest to the courtyard) and you'll run into it. Pick up the Ring of Invincibility, then go to the west-side meandering passage. When you entered that hidden area, two new areas opened up along the passage on this side. One has Wings of Wrath; in the other is another exit portal which goes to this episode's secret level, the Mausoleum. After enjoying a fly-around and collecting items, return here. The upcoming secret level is one of the best and most interesting levels of the game.