Ultimate Doom Easter Egg - Hidden Nine Inch Nails Symbol in E4M1

I. The hidden symbol can be found in E4M1, which is the very first level in Episode 4: Thy Flesh Consumed. The level is called "Hell Beneath".

II. Work your way through the level until you reach the room where you'll obtain the Blue Skull Key (the room behind the door locked by the Red Skull Key; its left from where you first start the level).

III. As you enter the room, there is a large rectangular metal column in the middle (with the Blue Skull Key just behind it). Go to the left of that column and you'll see a red torch (just like there is on the right side, but this one is special). Press the red torch (as if you're opening a door) and the large rectangular metal column will lower, revealing a NIN symbol on the floor and ceiling (the third N is backward). WARNING - You will also come under attack by four Barons of Hell (regardless of difficulty) as they teleport into the room.

* - Now to explain the significance of the NIN symbol: this is a symbol of the rock band Nine Inch Nails. They worked with Id Software (the creators of Doom, Quake, etc) to create the music for Doom. Trent Renzor of Nine Inch Nails also helped to create the original music for Quake too; you'll notice the NIN symbol on the Nail Gun ammo boxes).

NOTE - If you walk onto the symbol, you'll activate a trap. The side floor of the room will rise, trapping you in the room. There is a visible switch will appear that will lower the side floors, allowing you to leave the room. Its best the kill the barons before stepping onto the symbol.