Walk out of the small cave you begin this level in, and you'll see you're in a very long iced-over canyon. Various walls divide parts of the area into meandering pathways. A lava river runs the length of the canyon, with a high battlement along the other side. Outside the cave to your right you'll find the Green Door. At the far end of the canyon is a temple.
Fire and ice
Thoroughly explore the area. Be sure to cover all the pathways among the walls: there are several items around, plus you'll find the Yellow Key. There are assorted enemies around. Keep an eye out for Disciples of D'Sparil up on the battlement and around the temple. Occasional long-distance weapons fire from them can be a problem. Along the river there's a low cave with an Ethereal Crossbow. When you enter this cave, another cave upstream opens, with a Tome of Power inside.
Go to the temple at the end of the canyon. The entrance is the Yellow Door. (If you didn't find the Yellow Key, go to the left of the temple and start following the canyon wall, keeping the wall on your right. You'll come to it before long.) Enter the temple, go up the steps and get the Phoenix Rod. (If you didn't get the hidden one in the previous level, this will be a new weapon for you.) While on the steps, turn around and look back to the entrance. To the right of the door, in the corner, a teleporter has opened up. Enter it, and you'll be up on one of those high platforms alongside the temple. Watch out for the Disciple of D'Sparil if you didn't kill it earlier. Before jumping down, look for the stained-glass window in the temple wall nearby. If you looked around here earlier, you probably saw an Inferno Orb (this is ten rounds of ammo for the Phoenix Rod) out of reach on the window ledge. You can now reach it: jump down to the ledge, collect it, then go back in the temple. In the corner on the opposite side of the door from the teleporter, a second teleporter has opened. This one goes up to the platform outside on the opposite side of the temple. The Green Key is here. Like with the other side, there's an Inferno Orb on the window ledge nearby.
With the Green Key, go to the other end of the canyon, where you began the level, and open the Green Door. Inside here is a small cave with a teleporter leading up to the battlement. From up here, you can see that the battlement guards a huge area with several buildings, under a very wide and deep overhang. Jump down and clear out enemies. You'll find the Blue Door to the left, not far from the battlement. The two buildings closest to the battlement will be closed up for now. As you fight enemies, you'll attract the attention of Gargoyles in the buildings, many of which will fly out. This, and shooting the enemies you can reach through the windows, will simplify things when you're inside.
Go inside the large building. There are several entrances: the large front door, two side doors to the left and a side door around the side to the right. Inside the front door is a very large room with a big lava pool. (Wouldn't this be a fire hazard?) The stairs off to the left go up to a long U-shaped hallway, from which that side of the building is accessed. Next to the stairs is a doorway that leads only to the two left-hand side doors. You'll see one end of the U-shaped hallway out of reach above. On the right side of the large room is another doorway like the one on the left, except on this side of the building there are several rooms. Explore the area: there are several items available.
Go upstairs to the U-shaped hallway, and explore all the rooms along here. At the end near the left-hand side doors is a Map Scroll. Beginning at this end, in the first room is a switch. Hit this, and the doors to the medium-sized building will be opened. The other two rooms have items and armor.
Go now to the medium-sized building. Inside is the Blue Key. Explore in here: there's a Dragon Claw off in one corner. Before going to the Blue Door, go to the smallest building, which is now open. The Wings of Wrath are inside. After you're done, go back outside and open the Blue Door. A passage leads up to an interesting, large circular room. Take a look at the automap and you'll see that the symbol in the center, where the Hellstaff is, is shaped like a big eye. There are items on the dark ledge surrounding the room. A second passage near the first continues up, ending at the door to the room with an exit portal. This is the "official" exit, continuing to E2M5: The Catacombs, but this isn't the way you want to go...
Secret Level Alert
This episode's secret level is accessed from this level. Go back to the medium-sized building where the Blue Key was. Inside, a room with a teleporter is now open. This goes back up to the battlement. From here, jump down past the lava river to the iced-over area, and go to the temple. Earlier, you probably remember seeing a closed door behind the steps. This is now open. Inside is a passage to a second exit portal, this one leading to the secret level: The Glacier. It's an especially nice level so don't pass it up. (Unfortunately, you won't get to take the Mystic Urn in front of the exit portal with you if you already have one.) Before exiting, use your Wings of Wrath if you haven't yet: this level is especially enjoyable to fly around in.