Primary Excavation: Artifact Dig

Primary Excavation: Artifact Dig is the twenty-seventh and final level of Doom 3. The player must defeat the fourth and final boss, the Cyberdemon, in order to seal the Hell portal. An exploratory player may find the hidden "id Software" PDA, containing messages from several id Software employees.

Easter Egg
(Note: This Easter Egg can only be found using the God Mode cheat.) When facing the CyberDemon, enter the God Mode cheat and jump into the "wormhole" in the center. Crawl all the way down until it ends. At the very end, there should be an ammo pack, a health pack, or some other beneficial item. I have found different things, as they seem to appear at random. Another cool little tidbit is while all the way down in the very pit of the "wormhole", you can turn off the God Mode cheat and not get hurt. You will die if you try to get out without the God Mode on. There is also another weird thing. While battling the Cyberdemon, put noclip mode on, and go through the left wall, and keep going. If you went far enough, you will be in the beginning of Hell.