This last episode can get very messy, especially on Ultra-Violence where the first levels will be real pains with just a pistol. Not only this, but some of the levels are difficult in puzzles too. However, I guess it is set in Hell, so...

E3M1- Hell keep (Keep?! The only time it's well protected is on Ultra-Violence!)

i. Press the switch in front of you.
ii. Head N and press the left-hand switch to open the door
iii. Head NE through a door to another courtyard.
iv. Head through the E door and follow the long hallway to an area with some red pillars.
v. Head N through two doors then enter the teleporter to finish the level.

E3M2- Slough of Despair

i. Keep to the left-hand wall at the start and just keep running along it until you find the blue key.
ii. Go SE then N into another opening to find what looks like a dead end.
iii. Approach the wall and then avoid or kill the lost souls to reach the blue door.
iv. Enter the door, press the switch then go into the soul room and head N into the exit.

E3M3- Pandemonium

Blue key

i. Head N then go up the stairs.
ii. Go to the NE corner of this largish room and go up the stairs.
iii. Head S at the top, then follow the passage around to another junction, go S again.
iv. Drop down and go SW to find a metal room that houses the blue key.

Escape

i. Go upstairs from the blue key room.
ii. Go straight ahead and press the switch.
iii. Run through the next corridor to return to the largish room. (If you fell of the platform, retrace your steps to the start room)
iv. Go back to the start room. (unless you're already there, in which case go to step v)
v. Go W (you could also go E but it's a little harder)
vi. Keep going N until you reach a room with a skewered body.
vii. Go E through the 'archway' then immediately N upstairs.
viii. Go E through the blue door then N through to the exit.

E3M4- House of Pain

Blue key

i. Go S upstairs and follow the twisty corridor around to a door.
ii. Go S and press the W most switch or the switch on the far right.
iii. Go through the SW passage then continue W into the stone room.
iv. Go S as far as you can, then go E to get the blue key.

Yellow key

i. Go W then N to the door with the barrels.
ii. Go E through the door that looks like a computer circuit board.
iii. To open the N door, step in the water pit, then quickly run through the open door.
iv. Go through the tunnel until your reach two red pillars with switches, I'll call them the left-hand and right-hand pillar from how you can see it now.
v. Press the W switch on the left-hand pillar, then go through into the NW room and grab the yellow key.

Red key and beyond

i. Press the E switch on the right-hand pillar then go through the NE room and open the yellow door to get the red key.
ii. Press the S switch side on the right-hand pillar, then go through the E room and into the red door.
iii. Follow the passage around, through a red health draining passage to a switch.
iv. Drop down off the platform and go through the SE door.
v. Follow the corridor round and go through the exit door.

E3M5- Unholy Cathedral

Blue key

i. Go N slightly, then go W as far as you can.
ii. Go N through 3 set of doors.
iii. In the room with 3 pillars, go through the NE most door (not the one with the teleporters), then go through the E door.
iv. Go NE and walk through the red 'box' to open the door.
v. Go N through the door, carefully press the NE switch and then go into the NW corner to get the blue key.

Leave

i. Dodge the SW crusher and enter the teleporter.
ii. Kill or avoid the demons and go through the S door.
iii. Go SE then E through the blue door.
iv. Head W into the exit.

E3M6- Mt Erebus

Finishing the level

Easy skill levels (1, 2 & 3)

i. Head E then go NE over the lava.
ii. Head N to get the blue key.
iii. Go slightly NE to find a radiation suit.
iv. Grab the suit and go to the NW area of the map to find a building with a small entrance that will take you to a blue key barrier.
v. Go through the barrier to the exit.

Hard skill levels (4 & 5)

i. Go to where the blue key is on easier skill levels (near the caged imps).
ii. Go into the building and open the secret door near the SW candle.
iii. Jump into the red box and go into the teleporter.
iv. Turn around then go to the SE corner of this building to get the blue key.
v. Go to the western area of this building and press the switch, then go to the NE area to escape the building.
vi. Go NW to find a radiation suit.
vii. Go S around the grey stone building into the small entrance, and around through the blue barrier to the exit.

E3M7- Gate to Limbo

Blue and Red keys

i. Go N into the large chamber, then through the W opening.
ii. Head S then SE into the larger room. Cross either mini-bridge to get the blue key.
iii. Retrace your steps back to the large blood filled chamber, but go through the E opening this time.
iv. Go through the N blue door and go up the stairs to the W.
v. Go N and drop through the hole.
vi. Grab a rad suit and go W through the door.
vii. Continue W through to the next 'safe' room and go through the W opening in that room.
viii. When you can see the teleporter in the blood maze, go S then W to get the red key.

Yellow key

i. Go back to the large blood-filled chamber and go N through the opening. Grab a rad suit to the right
ii. Go through the western red teleporter in this room.
iii. Press the switch then go back through the teleporter.
iv. Go through the other teleporter in this room and grab
the yellow key.

Exit

i. Go back through the teleporter and then go to the blue key area. Go W to find another teleporter.
ii. Go forward and press the switch then go back through the teleporter.
iii. Go to the large chamber and go through the teleporter in the center of the room.
iv. Cross the bridge and open the yellow door, then press the switch.
v. Go back through the teleporter then go to the room W of the large chamber.
vi. Head through the NE passage in this room and enter the teleporter here.
vii. Open the yellow door, then cross the bridge to the exit.

E3M8- Dis

Finish the Original doom!

i. Open the door and walk or run down the hallway.
ii. Turn right to fight the final boss...

HINTS FOR THE SPIDER MASTERMIND

1. Take out the BFG9000 and you should kill it in 3 shots.

2. On harder difficulty levels, get the monsters to fight
the spider to weaken it.

3. Hide behind the central pillar, taking potshots every
now and then.

I find this level on Ultra-Violence easier then the
other skill levels, but that may just be me.