The Fortress of Doom is a space station used by the Doom Slayer as his personal headquarters. It was designed by the people of Argent D'Nur but built around a core of Maykr technology, originally intended as a base of operations for the Night Sentinels: it is implied to be one of many such structures, though the fate of the others is unknown. VEGA describes it as a "flag-station," implying it is a particularly large or well-equipped example of a Sentinel warship.
The Fortress is initially operated by the backup copy of the AI VEGA that the Slayer made before overloading VEGA's original core. Later this is switched for the consciousness of Samuel Hayden after the Slayer disconnects VEGA but still requires control of the station.
The Khan Maykr still retains some degree of control over the station's systems and attempts to trap the Doom Slayer by shutting off its power, but had not planned on the Slayer being able to use the Crucible he recovered during the events on Mars as an auxiliary power supply.
The Fortress is not technically a spaceship as it has no conventional engines; instead it uses an unknown form of space-folding technology based on Sentinel Energy to reposition itself while remaining stationary.
The upper level of the Fortress consists of the bridge at the front of the station, with computer consoles and a main viewscreen. Aft of this are a couple of terminals of which create the Freeze Bomb and Flame Belch equipment items, and two interface terminals which are later used to hold the remains of Samuel Hayden, and the first Crucible.
The second deck down contains the Slayer's personal quarters, a fabrication machine that creates the Ballista, and a number of locked chambers at the rear of the station containing useful items. Directly forward of these chambers is a locked cage containing the almighty Unmakyr, requiring six Empyrean Keys to open. Exits to the sides provide access to the two side-towers which contain the 2016 Praetor Suit and the Sentinel Training armor, though one has a partially destroyed access walkway.
The lower level includes side-chambers with more items, a destroyed Atlan mech torso in some kind of service gantry, and an elevator to the bowels of the ship where the Slayer maintains a demon prison as a training area, dubbed the "Ripatorium."
The Slayer's personal quarters, located at the front of the ship on the second deck down, are filled with Easter eggs, mostly references to games by id Software or Bethesda, or those with some relation to the Doom series. Bethesda describes these kinds of 'secrets' as an example of how great games "transcend universes."
- Flynn Taggart is referenced three times: a log-in credential in the computer that unlocks Doom 2, a biography/story book about him, and a company that bears his family name, Taggart Comics Group. There is also a couple of books written by Jill Lovelace, the other character from Doom novels, Knee-Deep In The Dead and Hell on Earth. Both of these books also refer to the novels based on the original Doom dilogy.
- Commander Keen's skull and blaster on the bookshelf, which is also portrayed on one of the collectible vinyls.
- A Soul Cube from Doom 3 is found on the Slayer's main computer desk.
- Original PC big-box copies of Quake, Quake III: Arena, Doom (two different boxes) and Doom II, along with a copy of The Art of Doom.
- Wolfenstein and Quake games are also referenced by various books and vinyls.
- Doom Guy's skateboard from Tony Hawk Pro Skater 3.
- A painting of the Slayer holding his pet bunny Daisy, as well as a rabbit cage and a bag of food.
- After collecting records, posters for each can be found throughout the base. These tell the name of the song, and who wrote them. Some are from Wolfenstein, Commander Keen, the Quake series, and others from various Doom games (including Doom 64).
- On the Praetor suit workstation's table a copy of Guns & Bullets can be found, a reference to a magazine in the Fallout universe.
The books on the shelf have a wealth of references. The top shelf are mostly parodies of well-known novels with Doom-themed words added:
- Dungeons & Demons - 6th Edition (parody of the tabletop RPG Dungeons & Dragons. At the time of the game's release, 5th Edition was the latest)
- The Count of Kadingir Cristo (parody of The Count of Monte Cristo by Alexandre Dumas)
- Eat. Rip. Tear. (parody of Eat, Pray, Love by Elizabeth Gilbert)
- Fifty Shades of Slay (parody of Fifty Shades of Grey by E. L. James)
- Slayenstein (parody of Frankenstein by Mary Shelley)
- Don Slayote (parody of Don Quixote by Miguel de Cervantes)
- Slayerhouse Five (parody of Slaughterhouse Five by Kurt Vonnegut)
- My Best Fiend, Daisy (possibly not a reference to any specific book, though it references Doomguy's pet rabbit, Daisy)
- The Ripping Tree (parody of The Giving Tree by Shel Silverstein)
- The Guts of Wrath (parody of The Grapes of Wrath by John Steinbeck)
- The Man in the High Argent Tower (parody of The Man in the High Castle by Philip K. Dick)
- How to Stop Worrying and Start Slaying (parody of How to Stop Worrying and Start Living by Dale Carnegie)
- The Slayer's Tale (parody of The Handmaid's Tale by Margaret Atwood)
- The Art of Rip and Tear (parody of The Art of War by Sun Tzu)
- The Power of Positive Ripping and Tearing (parody of The Power of Positive Thinking by Norman Vincent Peale)
- The Very Hungry Cacodemon (parody of The Very Hungry Caterpillar by Eric Carle)
- Demon Farm (parody of Animal Farm by George Orwell)
- The Great Gutsby (parody of The Great Gatsby by F. Scott Fitzgerald)
- To Kill a Mockingdemon (parody of To Kill a Mockingbird by Harper Lee)
- 1984 Dead Demons (parody of 1984 by George Orwell)
- Green Eggs and Pentagram (parody of Green Eggs and Ham by Dr. Seuss)
- The Caco in the Rye (parody of The Catcher in the Rye by J. D. Salinger)
- The Picture of Dorian Slay (parody of The Picture of Dorian Gray, by Oscar Wilde)
- Atlas Ripped and Teared (parody of Atlas Shrugged by Ayn Rand)
- How to Win Friends and Kill Demons (parody of How to Win Friends and Influence People by Dale Carnegie)
The books in the middle shelf contain more direct references. From right to left, these are:
- "My Buddy Superfly" by Hiro Miyamoto - John Romero's Daikatana
- "Why I'm So Great Part II" by Dork Norkem - Duke Nukem
- "Devilish Daggers & Other Assorted Pointy Objects" - Devil Daggers, an indie game based on Doom and Quake
- "LIANDRI - A Brief History of Interplanetary Industry" - Unreal
- "Von Braun - Onboard AI System Technical Manual" - System Shock 2
- "Mesa Science Monthly: Predicting Unforeseen Consequences" - Half-Life
- "U-NAT-CO Training Manual: Bomb Defusal" - Deus Ex, specifically a reference to the "Oh my God! JC! A bomb!" meme
- "The Spear of Destiny: A Post-War Deconstruction" - Wolfenstein: Spear of Destiny
- "Living With Rage and Other Common Emotions in the Apocalyptic Wasteland" - Rage
- "The Strogg: A Transdimensional Field Study - Quake II (and 4)
- "RET-CONNED: The Life and Times of Flynn Taggart" - Doom novels
- "From Nopefish to Dopefish: The Dope Tale" - The Dopefish
- "Tei Tenga - Offworld Travel Guide" - Doom, reference to Tei Tenga
- "Cooking from Hell's Kitchen - Thy Flesh Consumed" - The Ultimate Doom. Also, a reference to the reality TV show Hell's Kitchen.
- "2 Prey or Not 2 Prey" - Prey, specifically the cancellation of the original Prey 2
- "Vault Dweller's Survival Guide - Preparing Yourself and Your Loved Ones For the Inevitable Nuclear Apocalypse" - Fallout
- "How to Comb Your Mustache" by Cliffton M. Fischbach - Late father of popular YouTuber Markiplier.
- The above replaced "Nuka Cola - A History from the Atomic Age of Flavor" seen in pre-release screenshots, a second reference to Fallout