[[quoteright:175:[[http://www.worldofjapan.net/2011/11/unlucky-numbers-in-japan/ http://static.tvtropes.org/pmwiki/pub/images/Missing_floors_6301.jpg]]]]
[[caption-width-right:175:[[ThirteenIsUnlucky No thirteenth floor here.]] [[FourIsDeath Or fourth. Or fourteenth]]. [[ComicallyMissingThePoint Or Zeroth]].]]

->''"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''!"''
-->-- '''Creator/MitchHedberg'''

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. Typically either [[AWizardDidIt magic]] or [[ClarkesThirdLaw sufficiently advanced technology]] is involved in keeping such a floor hidden. 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, [[ThirteenIsUnlucky thirteen is a fairly common choice]].

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!!Examples:

[[foldercontrol]]

[[folder:Anime & Manga]]
* In both ''Anime/ReadOrDie'' 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 ''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 ''Franchise/OnePiece'', 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 [[TheHero 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 [[spoiler:such as Crocodile and Jimbei]]. 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 ''XXXHolic'', 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. [[spoiler: When the owners tore down the wall they indeed found another room, which had the words 'FATHER LET ME OUT!' scrawled all over the walls in blood.]]
* In ''EdenNoOri'', while Akira and co. were in [[spoiler: the pyramid]], they encountered a staircase which had a missing floor. It ended up being a double-floor room for [[spoiler: huge generators]].
* The fifth ''KaraNoKyoukai'' movie contains a variation in that it's an entire half of a building that's hidden through the use of an elevator that slowly rotates as it ascends and deposits you on the opposite side of the building than you expected. This is so [[spoiler:Araya Souren]] can carry out a magical experiment [[spoiler:with {{Artificial Human}}s in one half the building reenacting their last day alive and their original (dead) selves in the other, with their original brains located in the basement powering the whole system]].
[[/folder]]

[[folder:Comedy]]
* Comedian Creator/MitchHedberg commented that some hotels don't have a thirteenth floor due to superstition and hates to break it to them but the fourteenth floor is the thirteenth floor -- it makes no difference.
[[/folder]]

[[folder:Comics -- Books]]
* In the pre-Crisis Franchise/{{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.
* In {{New 52}} ''Franchise/{{Batman}}'' comics, it turns out the [[ComicBook/NightOfTheOwls Court of Owls]] has secret bases between the floors of various buildings in Gotham City, including several owned by the Wayne Foundation.
* In ''ComicBook/PaperinikNewAdventures'', the Ducklair building has 150 floors, officially. In reality, there is a 151st.
[[/folder]]

[[folder:Fan Works]]
* [[http://www.fanfiction.net/s/1657629/1/Harry_Potter_and_the_Power_of_Time 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, [[LaserGuidedAmnesia Obliviates]] several people to make it look like [[ThirteenIsUnlucky there was never a thirteenth floor]], and puts said floor under Fidelius.
[[/folder]]

[[folder:Films -- Live-Action]]
* The entire premise for the movie ''Film/TheThirteenthFloor'' hinged on this.
* The protagonist of the film ''Film/BeingJohnMalkovich'' works on Floor 7 1/2. It isn't a secret or anything, it's just an [[{{Bizarrchitecture}} 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.
* ''Film/TheMatrix 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 ''Film/{{Brazil}}'', the protagonist reaches a hidden floor by entering a sequence of buttons that play the recurring title motif.
* Implied in ''Film/NoCountryForOldMen'' when ProfessionalKiller Carson Welles is talking to his employer (note that this doesn't stop [[TheGrimReaper Anton Chigurh]] from finding and killing Welles' employer later on).
-->'''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.
* In ''OhGod'', protagonist Jerry Landers first talks to God on the 27th floor of a building that has only 17 floors.
-->'''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.
* Creator/ArnoldSchwarzenegger is infiltrating TheMafia in ''Film/RawDeal''. 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 corporation running the hotel in ''Film/FourteenOhEight'' believes that ThirteenIsUnlucky, so they pretend there's no 13th floor. Hence the thirteenth floor is re-numbered as 14 (just as is the case in many real-world hotels).
* 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. [[spoiler:A cult worshiping said maniac continues to murder people there.]]
* ''Film/{{Red}}''. BruceWillis' character is sneaking into a CIA file room that's so secret most agents don't know it exists. He gets into the elevator and presses the bottom button marked P2, holding his finger there as the floor indicator goes past that number to P3, B1 and finally B2 before the doors open.
* ''Hidden Floor'', a Korean horror film, takes place in an apartment building haunted by spirits that dwell on the supposedly non-existent [[FourIsDeath fourth floor]].
[[/folder]]

[[folder:Literature]]
* The ''Literature/WaysideSchool'' 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, one character {{Lampshade|Hanging}}s 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 CallBack to the beginning of the book).
* In ''[[Literature/VorkosiganSaga Mirror Dance]]'' by LoisMcMasterBujold, the Durona Group has a set of secret subbasements (in which [[spoiler: they store the protagonist while they're resurrecting him after cryogenic suspension]]).
* Platform 9 3/4 from ''Literature/HarryPotter'' is a variation, accessed by walking through the barrier between platforms.
* Level 13 of ''Literature/TheHitchhikersGuideToTheGalaxy'' building in ''Literature/MostlyHarmless'' 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 wrote a poem "A Tale of the Thirteenth Floor" in which a would-be murderer gets into an old-fashioned elevator, with an operator, in a hotel. The operator chooses to stop at the 13th floor -- to show him murderers chained to the corpses of their victims in a ghastly dance of damnation. (The whole hotel is kind of hellish, but the 13th floor is true Hell). The point is made, the plan abandoned.
* In ''[[Literature/AFableOfTonight 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 TimePortal.
* ''TheWarAgainstTheChtorr''. The [[GovernmentAgencyOfFiction 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 TwentyMinutesIntoTheFuture 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 [[PsychicPowers ESPionage]] group [[TheMenInBlack 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"[[note]]This is a ShoutOut to the ''Literature/JamesBond'' novels where 007 worked for a front company for the UK Government called "Universal Exports".[[/note]].
* The home base of the Moscow Literature/NightWatch is in a hidden floor, not normally accessible and [[AWizardDidIt not noticeable from the outside by non-magicians]].
* In the ''PercyJacksonAndTheOlympians'' series, Mount Olympus is accessed through the 600th floor of the Empire State Building.
* In the ''StarTrekATimeTo'' series, the Federation embassy on Qo'nos has a secret subbasement.
** In book 7, ''A Time to Kill'', [[SecretPolice Section 31]] has a listening post there. [[spoiler: The listening post is moved elsewhere after Ambassador Worf visits it; although he's the Federation ambassador to the Klingon Empire post-''[[Series/StarTrekDeepSpaceNine Deep Space Nine]]'', he isn't supposed to know about the post.]]
** 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.
* ''Fire World'', the sixth book in the ''Dragons'' (a.k.a. Last Dragon Chronicles) series, features a massive Librarium, in which the only way to navigate between floors is to imagine your destination. Floors beyond the 42nd floor are inaccessible to all but the very best.
* ''Literature/TheDayOfTheJackal''. The OAS leaders hiding out in a hotel in Rome create one by renting the top floors and [[WeldTheLock welding shut the lift doors]] on all but one floor, which is guarded by their men.
[[/folder]]

[[folder:Live-Action TV]]
* ''Series/ThePretender'' 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.
** Although strictly speaking almost everything in the Centre took place on 'missing floors'....from the outside the Centre was just a few stories tall, but it had 27 floors underground. The part above ground was used for counseling and legit psychological testing, and the basement sublevels were used for all the illegal stuff. It's just that SL-27, the very bottom sub-level, was even secret from most of the people who worked there.
* On ''Series/BabylonFive'', all the levels in sector Grey beyond 16 are mislabled with Grey 17 actually being the 18th level and so on. The actual 17th level had been sealed off during construction of the station and the elevators programmed to stop according to the new numbering system. Since sector Grey consisted entirely of the station's industrial facilities that were only visisted by maintainance crews, it took four years before anyone noticed that the elevator takes twice as long to get from level 16 to 17 than between all other levels. [[spoiler:The hidden level was used as a hideout by a doomsday cult who sealed themselves in with an alien monster.]]
* In ''Series/{{Angel}}'', the "White Room" in Wolfram and Hart is accessed by pressing a specific set of buttons in the elevator.
* The last season of ''Series/TheA-Team'' had an episode where Murdock is infiltrating a mental hospital. He and Hannibal discover a secret floor because the elevator takes longer than usual to go between particular floors.
* In the eponymous ''AreYouAfraidOfTheDark'' 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.
* ''TheRockfordFiles'' episode "Sticks and Stones May Break Your Bones, But Waterbury Will Bury You."
* The ''[[Series/TheTwilightZone Twilight Zone]]'' episode "The After Hours" has a 9th floor in a department store that's less than 9 stories high. [[spoiler:It's where the store mannequins hang out when they're waiting to have their month out among living people.]]
** The Devil has a travel agency on the 13th floor in "Of Late I Think of Cliffordville".
* One ''Series/IDreamOfJeannie'' 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.
* ''Series/{{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 ''Series/RedDwarf'', 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.
* ''{{Dollhouse}}''. Agent Ballard locates the building containing the Dollhouse, but after going on site can't find anything suspicious. So he does some research and discovers that in addition to the usual contractors the builders hired an environmental systems consultant, an expert in buildings that recycle their own air, water and power -- which you'd need for underground floors that you're trying to keep secret from anyone else in the building.
* In a rare example involving stairs instead of an elevator, in the ''Series/DoctorWho'' episode "The Lodger", people who go up the stairs to the second floor loft above Craig's flat tend to disappear. When Craig's best friend/secret crush Sophie visits the second floor loft, Craig and the Doctor follow her. Meanwhile Amy(who is stuck in the TARDIS outside of space and time) contacts the Doctor and informs him that she was able to find the plans for Craig's apartment building. "[[OhCrap There is no upstairs!]]"
[[/folder]]

[[folder:Video Games]]
* ''VideoGame/DeusEx'' gets a WhamEpisode moment out of revealing that [[spoiler:the secret Majestic-12 prison you've been trying to break out of is, in fact, the restricted-access-only bottom level of your employer's headquarters.]]
* ''Franchise/SilentHill''
** The [[FourisDeath fourth floor]] of Alchemilla hospital.
** Similarly, in ''SilentHill3'', 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 DarkWorld. 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 ''VideoGame/{{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 BigBad's office.
* ''VideoGame/TheJourneymanProject'': "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 ''GhoulSchool'' 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. [[GuideDangIt 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 [[spoiler:floor 0]]. 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 ''VideoGame/SpaceQuest 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.
* In ''VideoGame/GrimFandango'', Maximino's High Rollers' Lounge has an extra floor between its main area and the wine cellar. You need to figure out how to stop the kitchen elevator at the right point in order to get there. Also you can't {{Sequence Break|ing}} by getting in there before you know about it.
[[/folder]]

[[folder:Web Comics]]
* Appears in ''Webcomic/{{SSDD}}'', 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 ''Webcomic/{{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. [[spoiler:Makes for a good place to stash your [[DoomsdayDevice Doomsday Weapons]].]]
[[/folder]]

[[folder:Web Original]]
* On ''WereAlive'', the Tower is stated to be 15 stories tall but its really only 14 because [[ThirteenIsUnlucky there is no thirteenth floor]].
* ''WhateleyUniverse'' 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.
[[/folder]]

[[folder:Western Animation]]
* A ''WesternAnimation/FreakyStories'' story has an obsessive man trying to figure out the secret of a building's 13th floor. When he finally gets to it, [[spoiler:he finds that the door to the 13th floor locks from the inside, trapping him with everyone else who had discovered it.]]
* ''WesternAnimation/KappaMikey'' 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).
* This was used to great effect in an episode of ''WesternAnimation/TheRealGhostbusters'', 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.
[[/folder]]

[[folder:Real Life]]
* TruthInTelevision, sort of: some buildings actually do omit floor [[ThirteenIsUnlucky number 13]] or floor number 4 (the latter in Japan and China, since FourIsDeath there). This is just a renumbering to cater to the superstitious, though: the ''floor'' isn't missing, the ''number'' is.
** Some Chinese buildings go as far as to skip ''any'' floor number with 4 in it having the effect that you can buy a 50th-floor Chinese apartment in a 36-storey building.[[note]] Floors 4, 14, 24, 34, and 40-49 are all skipped.[[/note]]
** Due to its history, Hong Kong buildings can occasionally defer to [[ThirteenIsUnlucky BOTH]] [[FourIsDeath superstitions]]. The result? Well, see the photo at the top of this page. (yes, that particular elevator is in Japan, but it's more common to see 13 skipped in Hong Kong)
** 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. Because button panels were manufactured in a limited variety of sizes, elevators would often be installed with panels with more buttons than necessary. For example, in some buildings with ten floors only nine of them are served with the elevator, while the panel in the 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 DummiedOut) platforms.
** Terminals at John F. Kennedy International Airport in New York are numbered 1 through 8. Each terminal was intended to be used by a specific airline. 3 and 6 are skipped, as their primary tenants (Pan Am for the former, TWA and [=JetBlue=] for the latter) had eventually gone out of business and were subsequently demolished to allow other terminals to expand.
** 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 traditional superstitiousness of sailors.
* In Brazil, there is a TV station/college building (the Gazeta Building) that actually has a Floor 3. It can only be reached by one of the stairs, and no elevator stops there. Disappointingly, the only things on that floor are a few [=ATMs=] and a small bank agency.
* A building in Rotterdam, used by Dutch insurance company Nationale Nederlanden, has several of these. Certain elevators do not have a 1st or 2nd floor (ground being 0th in the Netherlands) because the entrance hall is three regular floors high, and some of the building's towers have service floors only accessible by a special separate staircase. Makes for fun times for an engineer who needs to service something but is unfamiliar with the building's layout.
* O'Hare International Airport in Chicago has four terminals, numbered 1, 2, 3, and 5. They skip Terminal 4.
** An explanation for this: Before the 1980s, there were just three terminals at O'Hare - Terminals 1, 2 and 3. Terminal 1 was for international flights and the other two terminals housed domestic airlines. However, in 1985, the original Terminal 1 was demolished and replaced by the current one (which today is used for United Airlines flights). So while the new United terminal 1 was being built, and until the current International Terminal opened on the east side of the airport, a temporary "Terminal 4" was erected on the ground floor of the main parking garage. International passengers would check in for their flights there and be taken directly to their aircraft by bus. It was used from 1984 to 1993 prior to the opening of Terminal 5 as the International Terminal. There is rumor that Terminal 4 might return if expansions and increases in air traffic at O'Hare justify the need for more terminals.
* Almost all airlines have seating algorithms where certain seat row numbers are skipped. Some noticeable instances:
** On all narrowbody United Airlines aircraft, some row numbers in the forward section of the Economy cabin are skipped so that rows 20 and 21 are always the numbers used for the overwing emergency exits.
** Lufthansa's Boeing 747-8 planes have two major number skips: First Class and Business Class on the main deck are rows 1-11 or -14. Then there's a skip to row 16 or 22 at the front of the Economy cabin. However, Business Class is actually split between the main deck and the entirety of the upper deck. The upper deck Business Class seats are numbered rows 81-88. Economy Class on the main deck ends at row 49, so there's a big number skip.
* Toronto Pearson International Airport has two terminals: terminal 1 and terminal 3. The former terminal 2 was replaced by a pier for Terminal 1 and was primarily used for transborder traffic to the United States.
[[/folder]]

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