Missing Floor

""My hotel doesn't have a thirteenth floor because of superstition, but come on, man. People on the fourteenth floor, you know what floor you're really on. "I'm in room 1401." No you ain't. If you jump out the window, you will die earlier!""

- Mitch Hedberg

Every building housing a top secret operation seems to have a "beyond top secret floor". There's no obvious button for it in the elevators, you can't reach it by stairs, and of course nobody has ever heard of it. Most realistic is a sub-basement, but it could also be higher than the highest official floor, or even squeezed in between floors - though in the last two cases, it's questionable how they've managed to keep it hidden at all, since anyone looking out a window could get suspicious. Finding it is a major plot point. It might have been closed off long ago (since it houses a Dark Secret) or it's still being used by the Beyond Top Secret club. In any case, don't expect to just walk in here, not even if you do have security clearance.

While it could technically be any number, thirteen is a fairly common choice.

Anime and Manga

 * In both Read or Die OVA and the sequel R.O.D the TV series, there's a secret bookstore that plays a role in the plot. It's hidden in the basement of a skyscraper, and can only be accessed by hitting the buttons in a specific order—unlocking a card-slot where the 'members only' card-key can be inserted.
 * The manga Oldboy concerns a prison where rich folks who want someone out of the way, but not dead, can pay dearly to have it done. It's set in a sub-basement accessible by only pressing two buttons on the elevator at the same time.
 * In One Piece, the World Government's great prison Impel Down has multiple underwater floors, with the prisoners assigned to a level based on how dangerous they're considered to be. Level 1, the closest to the surface, is for the least dangerous prisoners, while the most dangerous go to Level 5. When Luffy sneaks into the prison to rescue his older brother, the infamous pirate Ace, naturally he's assumed to be on Level 5. It turns out that Ace was actually being held on Level 6, a secret level where the World Government places even more dangerous prisoners . There's also Level 5.5, located between Levels 5 and 6, that was created by prisoners who escaped from their cells but had no means to escape from the prison itself.
 * In ×××HOLiC, characters are telling Ghost stories, and Himawari tells one of a hotel that was missing a room; from the outside, you could see the window that belonged to the missing room, but inside, the room was blocked off by a wall.
 * In Eden no Ori while Akira and co. were in, they encountered a staircase which had a missing floor. It ended up being a double-floor room for.

Comic Books

 * In the pre-Crisis Superman comics, the Daily Planet building supposedly had no 13th floor. In reality, the 13th floor existed and was secretly used by an alien tourist bureau dealing in vacations to Earth.

Fan Works

 * Harry Potter and the Power of Time (one of the first Independent Harry fics) has him looking for a place to live. So, he comes across an apartment house being built, Obliviates several people to make it look like there was never a thirteenth floor, and puts said floor under Fidelius.
 * In the Worm/Harry Potter crossover A Wand for Skitter, Voldemort's main base is inside the Ministry, occupying a floor erased from human memory and all records by a magical misfire during research by the Unspeakables. As it happened, if you were on that level when it disappeared, you remembered it -- and at least one of the Ministry staff who was so lucky was also one of Voldemort's moles.

Film
"Welles: You know, I counted the floors from this building to the street... Employer: Yes? Welles: And there's one missing. Employer: (dryly) We'll look into it."
 * The entire premise for the movie The Thirteenth Floor hinged on this.
 * The protagonist of the film Being John Malkovich works on Floor 7 1/2. It isn't a secret or anything, it's just an architectural oddity, accessed by using the emergency stop on the elevator halfway between floors 7 and 8 and then using the supplied crowbar to pry the doors open.
 * The Matrix Reloaded: "There is a building. Inside this building there is a level where no elevator can go, and no stair can reach. This level is filled with doors. These doors lead to many places. Hidden places. But one door is special. One door leads to the source."
 * In Brazil, the protagonist reaches a hidden floor by entering a sequence of buttons that play the recurring title motif.
 * Implied in No Country for Old Men when Professional Killer Carson Welles is talking to his employer (note that this doesn't stop Anton Chigurh from finding and killing Welles' employer later on).

"Jerry: How do I get to the 27th floor? Worker: In this building? Jerry: Yeah. Worker: I'm afraid you'd need a can opener. We only have 17 floors."
 * In Oh, God!, protagonist Jerry Landers first talks to God on the 27th floor of a building that has only 17 floors.


 * Arnold Schwarzenegger is infiltrating The Mafia in Raw Deal. In one scene he gets into a hotel elevator and tells the operator to take him 'down'. When the operator replies "There is no 'down', Arnie gives him a big tip and is taken down to an illegal gambling den.
 * The hotel likes to pretend that Room 1408 doesn't exist, "just as we pretend the 13th floor doesn't exist."
 * In Nightmare on the 13th Floor the hotel floor has been closed after a maniac murdered several guests many decades ago. On the outside the windows have been hidden with statues and other decorations. It's only accessible by using a special key in the elevator.

Literature

 * The Wayside School book series takes place in a 30-story school building. (It was supposed to be one story, with thirty rooms... The builder was very sorry.) Mrs. Zarves teaches on the 19th floor. The nineteenth floor doesn't exist. How can that be? The builder forgot to include it. Each book is thirty "stories" long, and in each book the nineteenth story is about Mrs. Zarves.
 * In the first book, the nineteenth chapter is simply "There is no Mrs. Zarves. There is no 19th story. Sorry."
 * In the second book, on character Lampshades this and wonders why the numbering isn't just shunted down after floor 18. She ends up stuck on the nineteenth story for three chapters, which are naturally chapters 19, 19, and 19. While there, she meets students that other characters made up in previous chapters. The next chapter fixes the numbering by being "Chapter 20, 21, & 22".
 * In the third book, the nineteenth chapter features Mrs. Zarves complaining about never being noticed, as well as a cow who won't leave her room (which is a Call Back to the beginning of the book).
 * In Mirror Dance by Lois McMaster Bujold, the Durona Group has a set of secret subbasements (in which ).
 * Platform 9 3/4 from Harry Potter is a variation, accessed by walking through the barrier between platforms.
 * Level 13 of The Hitchhiker's Guide to the Galaxy building in Mostly Harmless is hidden. Ford is so used to Earthly superstition that it takes him a moment to notice this. It turns out to be where the sinister new Guide is being made.
 * Ogden Nash's A Tale of the Thirteenth Floor.
 * In Stalking The Unicorn by Mike Resnick, every building in New York supposedly has one of these for its 13th floor, reachable by climbing stairs in the surrounding floors in an elaborate sequence ("It depends on the weather and the day of the week.").
 * In the children's book The Thirteenth Floor, the building is supposed to be one of the ones where the numbering just skips from 12 to 14... but when the protagonists manage to get into the thirteenth floor, it turns out to be a Time Portal.
 * The War Against the Chtorr. The Uncle Ira Group is located on the 13th floor of a hotel in Denver, reached by a private elevator. The first-person protagonist mentions that "controlled-access architecture" is nothing unusual in this Twenty Minutes Into the Future world, as hotels use them for guests who need extra security and privacy. You'd only realise it was there if you walked the fire stairs, and if asked the hotel would claim it was a service floor. They just wouldn't mention what service.
 * In the Necroscope saga by Brian Lumley, the ESPionage group E-Branch has their base on the top floor of a hotel. Although people working at the hotel—and anyone who cared to count the hotel's floors, go inside, and ask for a room on the top floor, and look at the floor number—know that there is a top floor, it has its own elevator and fire escape, and is stated to belong to a group of "International Entrepreneurs".
 * The home base of the Moscow Night Watch is in a hidden floor, not normally accessible and not noticeable from the outside by non-magicians.
 * In the Percy Jackson and The Olympians series, Mount Olympus is accessed through the 600th floor of the Empire State Building.
 * In the Star Trek: A Time to... series, the Federation embassy on Qo'nos has a secret subbasement.
 * In book 7, A Time to Kill, Section 31 has a listening post there.
 * In book 9, A Time for War, a Time for Peace, Worf puts the now-empty subbasement to good use as he retakes the embassy from a Klingon terrorist group.

Live-Action TV

 * The Pretender has sub-level 27, which became a major focal point for the series—as it progressed, it became hard to find anything that wasn't a result of something that happened on SL-27.
 * The episode "Grey 17 Is Missing" of Babylon 5 is about the "forgotten" version of this. Would have been better had it stayed forgotten...
 * This and The Real Ghostbusters episode cited below were both written by J. Michael Straczynski.
 * In Angel, the "White Room" in Wolfram and Hart is accessed by pressing a specific set of buttons in the elevator.
 * In the eponymous Are You Afraid of the Dark? episode, the thirteenth floor exists, but its occupants have long since disappeared. Turns out that the former residents are aliens, and they're coming back for their daughter, Karin.
 * The Rockford Files episode "Sticks and Stones May Break Your Bones, But Waterbury Will Bury You."
 * The Twilight Zone episode "The After Hours" has a 9th floor in a department store that's less than 9 stories high.
 * One I Dream of Jeannie episode has the main characters attempt to book a room in a a filled-up hotel, so Jeannie just magically creates a 13th story and books the room there, when the Bellows know that the hotel in question only has twelve floors. Cue much confusion from the hotel staff and the Bellows, while Tony and Jeannie simply denied that there was anything unusual about the floor at all.
 * Smallville has a fertilizer plant with a hidden sub-level 3. The 3 button on the elevator is invisible. More specifically, its a black marble button in a black marble control panel.
 * In Red Dwarf, Floor 13 is believed not to exist by most of the crew. It houses the ship's brig and is accessed by using a key to reveal a secret panel in the lift.

Video Games

 * Deus Ex gets a Wham! Episode moment out of revealing that
 * Silent Hill
 * The fourth floor of Alchemilla hospital.
 * Similarly, in Silent Hill 3, after the phone call in the hospital, you go through a Missing Door that wasn't there before, that leads you to the alternate hospital.
 * Several floors of the Office Building in Silent Hill 3 only exist, or at least can only be accessed in the Dark World. The sixth floor is not accessible at all.
 * The Evil Brookhaven Hospital in part 3 has three basement floors(two of which don't exist in the normal world), but only B3 is accessible.
 * The thirteenth floor in the Macintosh Doom clone Sensory Overload has no button in the elevator, and can only be accessed via ventilation ducts. Beyond that is the sub-basement, only accessible via the hidden express elevator in the Big Bad's office.
 * The Journeyman Project: "Access denied. This floor is neither modeled nor rendered."
 * In the forgettable 1994 adventure game Hell Cab, pushing a red button on the elevator in the Empire State Building would take you down to hell.
 * In Ghoul School for the NES, the left half of the school can only be accessed via the roof. To get there, you must get on the elevator, press up, and hold it down, at which point the elevator will shake as though resisting, then rise to the unmarked ceiling. There's no indication that you need to do this.
 * Tower of the Sorcerer has three. The first one is obvious, since the stairs from floor 42 go direct to floor 44. The intervening floor 43 can only be accessed by obtaining the "wings to fly up", which move you up one floor wherever you use them. There are also "wings to fly down", and one puzzle depends on using these to access . Finally, the floors come in groups of ten, but the highest floor accessible by stairs is floor 49. There is a floor 50, which you reach during the game's ending.
 * In Space Quest II, the elevator in Vohaul's space station has no 2nd floor button. To reach that area, you must solve a gauntlet of puzzles that require items from the other floors.

Web Comics

 * Appears in S.S.D.D., where a supposed "storage installation" in the middle of the desert hosts a top-secret research-lab in a hidden basement. Once again, it can only be accessed by hitting the elevator buttons in a specific order. Or by blasting the panel, apparently.
 * In Thunderstruck, every building that goes from 12 to 14 in their numbering still has a metaphorical 13th floor. Which a mage can enter and walk around in.

Web Original

 * Whateley Universe likes this one; all the cottages have at least one hidden basement floor, where they keep the exercise equipment and cottage vaults that Muggles shouldn't see or have access to, and the required display is hidden as well (because, after all, you don't want people just walking in and seeing that you've got several tons of gold just sitting around). And that's not even counting the hidden tunnels, and laboratories and workshops, and the testing areas that are all buried underground, too. It's Lampshaded in mentions that they have to be very careful about where they tunnel these days, or risk sections of the school falling into a sinkhole.
 * On We're Alive, the Tower is stated to be 15 stories tall but its really only 14 because there is no thirteenth floor.

Western Animation

 * This was used to great effect in an episode of The Real Ghostbusters, when Janine dons her 5th Ghostbuster gear to track down the missing quartet. She traces them to a building, but can't find them anywhere within it. When she rides the elevator, she notes the missing thirteenth floor but dismisses it as superstition, until she notices that it takes too long to go from floor 12 to floor 14. One emergency stop button and one proton-pack charged "lock-pick" later and she's found a ghost floor, complete with ghost receptionist.
 * A Freaky Stories story has an obsessive man trying to figure out the secret of a building's 13th floor. When he finally gets to it,
 * Kappa Mikey has a secret floor in Lily Mu Towers, which is accessed by pressing the buttons 9 and 4 (9+4=13). It is home to a mad scientist (who, according to Ozu, hasn't paid rent in 40 years).

Real Life

 * Truth in Television, sort of: some buildings actually do omit floor number 13 or floor number 4 (the latter in Japan and China, since Four Is Death there). This is just a renumbering to cater to the superstitious, though: the floor isn't missing, the number is.
 * This custom makes it a little more convenient for fictional entities wanting to make a "real" missing floor—since no-one expects to visit a floor numbered "13", they won't be surprised when the ordinary everyday elevators skip by that floor.
 * Many skyscrapers have dedicated mechanical floors used for heating/cooling units, electrical junction boxes and maintenance equipment storage. The horizontal bands on the former World Trade Center towers were a visible example. These types of floors are not typically accessed from the main public areas but usually count in the floor numbering. Of course, 13 is a popular choice.
 * This is quite common in Moscow. The reason is that there were limited set of button panels manufactured, so it was the only choice to install panel with extra buttons with no corresponding floor. For example, the building I live in has 10 floors, but only nine if them are served with the elevator. The panel in elevator has 10 buttons, however....
 * Moscow State University's Main Building has several 'tech floors' which are hard to get in (not mentioning top floors with restricted access). There are also underground tech rooms between Main building, Chem Building and Phys Building for sure and urban legends exist about even more hidden undergrounds there.
 * Many building from USSR times in Moscow have bomb shelters with hardly available entrance.
 * The Mount Auburn Hospital in Cambridge, MA has no sixth floor in its main wing. Or at least none that can be easily gotten to—none of the public elevators go to it, and its door is locked from the stairwell. It's mostly maintenance and engineering stuff.
 * In a subversion of this trope, back in the 1980s and 1990s, the elevators in Cincinnati and Hamilton County Library's Main Library building had floors numbered A, B, 1, 2, C, D, 3. Only the numbered floors were accessible to the public. The lettered floors were for the stacks. (There were also references in the building to a floor "M" (for Mezzanine) between the first and second floors, but it was only accessible via stair or wheelchair ramp.)
 * At the main station at Hannover in Germany the departure platforms 5 and 6 are nonexistent. However there is a rather unspectacular explanation for this: Track 5 and 6 are solely used for the transport of goods, and because of that a platform is unnecessary.
 * Some subway stations in New York and London have non-existent (or Dummied Out) platforms.
 * During the Cold War, East Berlin had a number of "ghost stations" (Geisterbahnhof) in places where U-Bahn and S-Bahn lines originating in West Berlin would briefly pass through East territory. Trains would pass through without stopping, and many of these stations remained deserted and unchanged from 1961 to 1990.
 * For decades during the Cold War there was a secret bunker beneath a wing of The Greenbrier resort in West Virginia, built in order to house the U.S. government in the event of nuclear war.
 * It's common for ships not to have a deck numbered 13 - maybe to cater to the superstitious clientele, maybe due to the mild superstitiousness of sailors.
 * In Brazil, we have a TV Station/College building (the Gazeta Building) that actually have a 3 1/2 floor. It can only be reached by one of the stairs, and no elevator stops there. In there, there is just a few ATMs and a small bank agency. (this trooper graduated from there and used that bank every now and then)