A subtrope of BiggerOnTheInside. A place looks fairly normal from the outside, and possibly even when you get in, it's of a reasonable size. But there's this door in the back. Open it, and... there's a whole new section of the place, easily as big or bigger than everything you've seen so far! And look - there's a door in the back of that too, which leads to yet another new section - or worse, ''five'' doors...

Basically, it's when BiggerOnTheInside keeps happening to the point of an OverlyLongGag. Related to BigLabyrinthineBuilding. Can be especially nightmarish in the MobileMaze, where you can also know that the rooms ''weren't'' there before.

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!!Examples:

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[[folder:Comic Books]]
* When ''ShadeTheChangingMan'' moved into a crack in the pavement of Times Square, it was already BiggerOnTheInside. New rooms appeared as the story required, and his son George spend months touring them.
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[[folder:Literature]]
* Arguably Death's Domain in ''Literature/{{Discworld}}''. The initial hallway is intimidating enough, but several of the rooms along it open up into cavernous chambers filled with books or hourglasses.
** The Unseen University library is definitely this. It extends into L-space. In ''Discworld/GuardsGuards'', we see it can even be used [[spoiler:to travel through time]].
* ''[[color:blue: House]] [[HouseOfLeaves Of Leaves]]''. The [[color:blue:house]] on Ash Tree Lane is this, having doors that open from the normal part of the [[color:blue:house]] to a seemingly never-ending sequence of cold, colorless rooms, hallways, and stairs, just like a ClownCarBase.
* The Room Of Requirement in ''Literature/HarryPotter''.
* Lady Door's house in ''Literature/{{Neverwhere}}''. It's got a nearly-infinite number of rooms, scattered across all of space and time. There's no need for a physical connection between them, as her family has the ability to open portals by touching anything that opens and some things that normally don't.
* John De Chancie's ''CastlePerilous'' series features Castle Perilous, a castle containing portals to 144,000 different universes.
* Morwen's cottage in the ''EnchantedForestChronicles'' appears small on the inside, but has a door that leads to a different room every time it's opened. Morwen's narration identifies four specific rooms (a library, a study, a magic workshop and a storage room) and "several" guest rooms, and notes that she can still add at least three or four more rooms before she'd have to add a second door. The door and its rooms weren't an easy project, taking considerable time and effort, but she considers it to have been more than worth every minute.
* The Godmothers hut in MercedesLackey's ''[[Literature/TalesOfTheFiveHundredKingdoms The Fairy Godmother]]'' looks like a normal cottage in the woods even from the first few rooms. Then you realize that there really shouldn't be room for two stories, a big kitchen, a pantry, a library, and several other rooms. Then, later in the book, Godmother Elena reveals the true nature of the totally not just a house. It's simply magic.
* The titular ''Literature/HouseOfManyWays'' follows the trope description almost to a T, but the door at the back is actually the door in the middle. What starts out as a house with two rooms and one inside door turns out to have two rooms, a dark hallway, and another hallway with bedrooms and a washroom, ''then'' is eventually revealed to contain part of the brownies-by-any-other-name's underground caves and [[spoiler:the entirety of the indoors of the royal castle a two-hour walk away]].
* Creator/CharlesDeLint's Tampson House in ''Literature/{{Moonheart}}'' and ''Spiritwalk'' is a good example. It's a mansion that takes up a city block, but looks like a series of townhouses from the outside. That's without going into how one can reach multiple spirit worlds from within it.
* ''Literature/TheNeverendingStory'' features a palace of doors which can lead to any portal in any world at any moment, though the entrance is constantly changing. It does work as a useful travel mechanism, though; each room has two unusual doors (like a giant zipper or a vault door), and to get to one specific place you have to go through the doors that remind you of things at your destination.
* The House of the Undying in ''ASongOfIceAndFire'', which deliberately invokes {{Bizarrchitecture}} as navigating it is part SecretTestOfCharacter and part VisionQuest. Daenerys first notices this when she finds herself climbing a large staircase, when the building she entered appeared to only be one storey high.
* ''AndHeBuiltACrookedHouse'' by RobertHeinlein. The house is a tesseract.
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[[folder:Live Action TV]]
* Though they rarely bother to show it anymore, the TARDIS from ''Series/DoctorWho'' has so many rooms even the Doctor himself isn't sure where they all lead (except for that time where they jettisoned part of it. He knows that door doesn't lead anywhere anymore).
** Has happened to a couple of houses in the new series, when aliens attached new rooms or floors to an existing building.
* This happens in the first episode of ''Series/TheGoodies'' when Greame is showing the other two around their new office.
* In TheITCrowd episode ''The Red Door,'' Jen suddenly becomes curious about the titular door in the corner of the office, which hasn't been shown on screen previously. At the end of the episode another, more terrifying door is briefly shown (and never mentioned again).
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[[folder:Music]]
* "House of Four Doors", by The Moody Blues
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[[folder:Tabletop Games]]
* In ''DungeonsAndDragons'', justified by the existence of other planes of existence having magic portals to them, sometimes cleverly disguised as a normal door.
** Baba Yaga's Hut in three different ''DungeonsAndDragons'' incarnations: the original in the 1E DMG, "The Dancing Hut of Baba Yaga" adventure in Dragon magazine #83, and the 2E module ''The Dancing Hut of Baba Yaga''.
* This can be a power of Manses, buildings that channel geomantic energies, in ''{{Exalted}}''.
* In ''BetrayalAtHouseOnTheHill'', rooms are added as you explore the building. Usually not all the rooms are found, and 'false doors' are possible - new rooms cannot be placed in a manner that the house cannot continue to expand - so it seems that the house does continue forever combined with ''MalevolentArchitecture''
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[[folder:Video Games]]
* Peach's Castle in ''[[VideoGame/MarioAndLuigiBowsersInsideStory Mario & Luigi: Bowser's Inside Story]]''. The initial castle area is large enough, but as you progress you keep opening up more and more areas, until it turns out to take up well over a hundred screens. Compare this to the entire Toad Town, which takes up ''five''.
* ''VideoGame/SuperMario64'', perhaps the ancestor of the ''[[VideoGame/MarioAndLuigiBowsersInsideStory Bowser's Inside Story]]'' example above. The room you walk into when you enter the castle seems to be about the size of the castle. However, more and more places open up. The basement makes sense. It could be under what we see from the outside. However, the upper levels are definitely an example of this.
* The player's house in ''AnimalCrossing'', once you start adding on extensions.
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[[folder:Webcomics]]
* [[http://aftertorque.com/comic.html Under Lock and Key]], a webcomic whose entire premise is this; every door can open into a totally random room in the house, and nobody knows how far it goes.
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[[folder:Web Original]]
* Wiki/{{SCP|Foundation}}-[[http://scp-wiki.wikidot.com/scp-167 167]], the aptly-named Infinite Labyrinth. There's also [[http://scp-wiki.wikidot.com/scp-184 SCP-184]], which does this to any building it's placed inside.
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[[folder: Western Animation]]
* The Classic ''ScoobyDoo'' thing where they are running from the bad guys, hiding in barrels or [[ScoobyDoobyDoors popping in and out of doors]], often uses this.
* In ''{{Futurama}}'', Fry spends a whole episode living in Bender's apartment - a room just big enough for two people to stand up in - before discovering a door in one wall which leads to the closet, actually a spacious apartment with several further rooms leading off it. The door wasn't even being hidden by clever use of camera angles or anything - it was a blank wall in all previous scenes.
* In ''KingOfTheHill'', the Hill family takes a vacation to Japan. In their tiny hotel room, they do all their cooking and sleeping in a space about half the size of their living room, as a parody of overcrowding in that country. However, at the end of the two-parter when Hank's brother comes to help them check out, it is revealed that that was just the sitting room; there was a sliding door leading to several other rooms, and even a fountain.
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[[folder:Real Life]]
* The [[http://en.wikipedia.org/wiki/Winchester_Mystery_House Winchester Mystery House]]. A huge, sprawling mansion with hundreds of rooms. At one point you think you've reached the end, but then you open the closet door and it opens on a whole new wing.
* [[http://www.unforgettable.dk/ 42.zip]], while mentioned on the BiggerOnTheInside page, probably fits better here. It's a .zip containing 16 more .zips, which each contain 16 more .zips, and so on and so on. At the very bottom of the chain is a 4.3GB file, meaning altogether it takes up ''4.5 petabytes''. That's [[http://en.wikipedia.org/wiki/Petabyte more than the entire Internet Archive and all the 3D rendering effects for Avatar]] ''[[http://en.wikipedia.org/wiki/Petabyte combined.]]''
* It's an old joke about housing in NewYorkCity that everyone is always secretly hoping they'll notice a door one day that they [[FailedASpotCheck never saw before]], and it turns out that their apartment is [[FriendsRentControl twice as big as they realized]].
* Many used book shops are like this, since they tend to be built into old houses. For example, one has a main room that many people never get beyond... despite the fact that beyond it, through a tiny opening, there are five more rooms of equal or greater size.
* Cave exploration often adheres to this trope, as a previously-documented cavern might turn out to have another ''huge'' series of chambers and tunnels attached to it when rubble is cleared or divers investigate a subterranean pool's depths.
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