- This level occupies the map slot MAP30. For other maps which occupy this slot, see Category:MAP30.
MAP30: The Lair is the second secret level of Doom 64, accessible from MAP12: Altar Of Pain. It contains the same background music as level 12, Altar Of Pain. This level consists of a medium-sized structure with an upper, open area and a winding basement that houses monsters of varying degrees of strength and, for all intents and purposes, this is where the player will first come across arachnotrons (if the player didn't already go through MAP32: Hectic). The objective of the level is to obtain the demonic Artifact. The intermission screen before this level states: "You smile. What strange place have you stumbled upon? The Demons did not expect you to survive this far. You feel their demonic presence waiting for you... Let them taste their guts!"
As in MAP29: Outpost Omega, the main objective in the level is to find the demonic Artifact, which is located in the center of the building atop a high pillar. In order for the player to get it, he must first head to a closed-off section of the upper deck to the right of the pillar (when facing it from the other end of the room), thereby activating a tripwire that lowers a portion of the far wall, exposing a shootable switch. After shooting it, the player must run to the adjacent section on the other side of the upper area where another shootable switch is located. Shooting that will lower the pillar, giving the player access to the Artifact. After this is accomplished, the player must then continue through the building into the basement, battle hordes of demons, and find the yellow key. This gives the player access to a switch which will bring about the exit, which is back in the starting room.
- In the room with the Demon Artifact, (after you've cleared out the enemies and revealed the stairs) go up the stairs and enter the smaller room on your left (relative to the entrance) with the wood floor. When you step on the floor you should hear a timed wall lower. Now stand right in the middle of the large window frame in this small room, look to your right, and you'll see a switch. Shoot it before time runs out, then turn to your left and look through the smaller square window, and you'll see a new switch has been revealed. Shoot that one, and the center pillar lowers, allowing you to get the Demon Artifact.
- Also in the room with the Demon Artifact; this time go into the small wood floor room on the right. From here, walk through the small square window near the center staircase. This triggers a small alcove near the entrance of the room to open, revealing a Plasma Rifle.
- After going down the descending spiral stairs, you find yourself in a sewer-like area. Follow the path ahead, killing enemies as you go, taking a left at the first fork, and stopping where the Box of Bullets is. Look to your right, and you will see an alcove with a gargoyle statue that is lit more brightly than the others. Get off the path, examine the statue, then turn around and cross back over the concrete path, go around the curved watery path, and you'll see a wall that has just opened up, leading to a Megaarmor.
- After getting the Megaarmor, go back to the brightly lit statue that activated the wall from secret #3, but this time just keep going past the statue down the watery path, and you'll see a Soul sphere that wasn't there before.
This level possesses a key activated tripwire, something that has never been used in a mainstream Doom title. The player needs to have the yellow key in his possession to activate the tripwire that will expose the exit-bringing switch; merely walking through without it will result in an "MMPH!" pushing voice and a message stating "YOU NEED THE YELLOW KEY".