This level, the last full-size one of the episode, is primarily made up of several buildings within a large area enclosed by a battlement, itself in a massive outdoor area surrounded by water. You begin outside at one end of the area; you can see that the battlement is surrounded by a wide area out of reach above the water. Work your way around the area, clearing out enemies. It's possible to reach the Ophidians up on the battlement, but not critical at this time. About halfway along the outer area you'll come to a second, much smaller battlement to your right opposite the main battlement, with a low water-filled tunnel leading inside. The tunnel is blocked by bars just inside; you'll find an Ethereal Crossbow. Just around the corner from the second battlement you'll come to a bridge crossing over to the upper area outside the main battlement. Here you'll find an entrance to the main battlement: the Yellow Door. Finish clearing out the enemies along the far end of the outer area, then return to the bridge. Most of the upper area to your right will be out of reach. Go left instead, around the battlement, and you'll come to another part of the upper area that's out of reach. Just before here is the Yellow Key.
Inside the battlement
Go back to the Yellow Door and go inside. Go through the whole area, clearing out enemies, most of which are Sabreclaws. You'll see a large inner fortress taking up much of the space inside, plus a large building near where you entered. In between the two is a courtyard with an out-of-reach pool. You'll find two more gates leading outside the battlement; these go to the upper areas that were unreachable from outside. There are many items in both areas. At the far end is a tall building and the Blue Door. Have a weapon ready when you go around to either side of the building: there are a bunch of Disciples of D'Sparil under the low overhanging areas alongside the building.
Near either side of the Blue-Door building, you'll find stairways leading up to the battlement, although most of it will be blocked by dark-metal barriers. Look for and hit the switch up one of the stairways, then go around behind the building near the Yellow Door. Earlier you probably saw a wooden stairway leading up to the battlement, but the lowest step was out of reach. The switch you hit raised that lowest dark-metal step, allowing access.
Go upstairs and explore this end of the battlement. Additional dark-metal barriers will be in the way. You can cross over the gap above the Yellow Door if you get a running start; likewise, you can jump to the big porch near the stairs. On the porch you'll find the Green Door down some stairs leading farther into the building (the pylons are at the top of the stairs). Look around the narrow section of the porch to the right of the Green Door, where there's a Mystic Urn hiding behind the columns. Back along the battlement, go over to the courtyard between the building and fortress, get into a suitable position and jump out and down into the pool, where you'll find the Green Key. When you jumped into the pool, the barriers on top of the battlement lowered, allowing access to the rest of it. There are loads of items along here, especially Flame Orbs. You can also get to the ledge surrounding the fortress and all the Runes with a running jump, plus you'll see another building inside the fortress.
Return to and enter the Green Door. The stairway continues down, and passes two doorways to the right, at the landing and near the bottom. First, look along the ledge to the left above the stairs, where you'll find a Map Scroll. At the landing is a couple side rooms with items. When you enter the side room near the bottom of the stairs, the lights will go out. Watch out for enemies in the dark. Find and hit the switch in here, then go back to the stairs and follow the passage ahead. It was a dead-end earlier; the switch uncovered a teleporter.
Enter the teleporter and you'll inside the fortress, outside the building. Circle the area, clearing out the enemies. You should be able to get to the ones inside the building through the windows. The teleporter you find goes back to outside the Green Door. There's a secret compartment nearby: at one end of the fortress, look along the center of the wall at the section made of gray stone that's sticking out a bit. You'll see the texture is slightly misaligned: activate this section to open a hidden door to the compartment.
In a small area along the building, there's a dark metal column. (Follow the wall of the building and you'll come to it.) Hit the switch on the column: this converts some of the windows in the building into doorways. Inside, you'll find a section blocked off by a wooden barrier you can see around a bit. Shoot at or strike the barrier, and it will open, and also a couple compartments with Disciples of D'Sparil will open. After fighting them, look around in the area just inside the windows/doorways that led into the building, and you'll find an item in one of the opened compartments. Note the wooden columns throughout the room. When you step into the area past the barrier you shot open, the columns will open, releasing additional enemies. Fight them, then go up the stairs past the barrier. Up here are Wings of Wrath and a second teleporter.
The teleporter goes to one side of the small battlement outside along the water. (The other side is only accessible by flying; there are items so be sure and go there sometime.) Find and hit the switch, then jump down and go to the water-filled tunnel. The switch opened the bars. At the end you'll find the Blue Key. There's a bonus inside the area that opened behind the Blue Key. Activate the wall to the left, in the corner where the hanging skull is. The wall, which is actually the near end of a long water-covered lift, will slowly lower a long way down, uncovering nooks on either side where there are items. Don't worry about reaching all of the nooks; the Gargoyles inside them will get in the way, and you'll be able to fly back to them afterward. The teleporter at the bottom goes to the outside of the inner battlement.
Go to and enter the Blue Door. In here is a tall room with four cages in the corners containing Disciples of D'Sparil, and a tall, short corridor at the far end leading to an area out of reach high above. Watch out for that red overhead structure inside the circle of columns: it's a crusher that will activate when you step under it. When you go for the armor in the center (you can safely stand here too) both sides of the room will open, connecting to the overhanging areas outside and releasing a few additional enemies. You can now get to the four cages and items that may have been dropped inside.
When the sides of the room opened, a section of the end of the corridor also lowered, uncovering a lift that will lower when you approach it, leading to another short corridor high above to the left. At the end is the level exit. Before leaving, if you haven't yet, remember the rest of the small battlement and the nooks (which all have Flame Orbs) inside the deep bonus area at the end of the water-filled tunnel. But the final level of the episode, coming up next, has a great deal of items so it's not critical to stock up here.