The Primary Excavation Site houses the ancient burial chamber. The discovery of this chamber unearthed the stone tablet, soul cube, and many other valuable artefacts.

You start off in a room with a ton of gear in it:

15 boxes of shells
3 shotguns
2 plasma guns
10 plasma canisters
BFG
7 ammo belts
3 packs of grenades
4 machine guns
15 clips
2 chainguns
3 rocket launchers
3 packs of rockets
2 suits of 50 armor
2 health packs (30 each)
Gear up and lock and load.

Head into the hallway. The path to the right looks like a dead end, but if you work your way over the wreckage, you'll find a BFG cell. Go back to the left and down the stairs. You'll see lots of construction and scientific equipment as you go. Eventually, you'll work your way to a room with a big coffin in it. A presentation will be playing talking about the ancient civilization. There are 2 health packs (15 each) on the desk near where the presentation is playing. Take them, and walk around to the back side of the coffin/sarcophagus. The wall will disintegrate and leave a door. You'll pick up a backpack (ammo) as you wal through. Turn right and follow the hall. Another wall will open up and you will walk into a square room. The floor will start to fall and will evetually stop, presenting another way out. Follow the path downward. You will evetually get to a long path downward that had 4 candles at the end of it (3 on one ledge, 1 on another).


DON'T TURN RIGHT if you want to go to the secret room. Instead, turn left and go to the back of the alcove. Crouch down and you'll see a stone that says "id" on it. Press it (you won't see a cursor) and a wall will open to your left. Walk through and pick up the PDA on the altar. It's for "id software" and has a lot of cool stuff in it. When you're ready to face the final boss, go back and turn RIGHT this time.

The final boss is the Cyberdemon. As the soulcube explained the first time you visited hell, it is the only way to defeat him. The strategy is simple. Kill normal demons until you get a soulcube shot. Use the soulcube on the Cyberdemon and repeat. You must hit the Cyberdemon with the soulcube 4 times. Demons spawn around the pit in the middle, so arm the shotgun (or whatever favorite weapon you have - I suppose the rocket launcher would be fun) and start running around the pit in the middle killing demons. Obviously, you need to avoid the rockets from the Cyberdemon. When you get your soulcube shot (once every 5 kills), be sure to hit the Cyberdemon - if a normal demon is between you and the cyberdemon, you may hit it instead, so be careful.

When you shoot the fourth time, the ending cinematic will play. Sequel, anyone?

Congratulations, you've beaten Doom III! Now for nightmare...