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One of the WorldShapes more often found in ScienceFiction than in {{Fantasy}}, a Ring World Planet is a world that is [[ShapedLikeItself a world in the shape of a concave cylinder]]. The horizon curves up, not down, but only in one dimension, meaning that the ground in that direction would be "uphill"[[note]]If gravity is generated by spinning the cylinder, it would only ''look'' like it was uphill. The surface would be "level" as far as walking, water flow, etc is concerned.[[/note]] unless the ring is large enough that the curve is impossible to notice over small distances. The sides of the cylinder will be walls, with or without a "ceiling." These can range in size from a true DysonSphere to a cylindrical space station. These variants of worlds usually at least pay some lip service to the known laws of physics, since a spinning ring generates a centrifugal force that could be used instead of gravity. However to exist for real, particularly large ones over a few dozen kilometers would have to be made of {{Unobtainium}}.

Note that it would always be "day" in such a cylindrical world unless measures are taken to simulate day and night, either through sun shades, mirrors, or some combination of the above. Another alternative is choosing an orbit where the ring periodicaly gets shadowed by something. Orbits that use the Earth for this would produce night about every 90 minutes (ISS altitude) or a few minutes every few months (a typical geostationary orbit, about the same frequency as a lunar eclipse).

These were formerly referred to as "Niven's Rings" by physicists, astronomers, and science fiction writers, after the creator of the concept, author Creator/LarryNiven (who thought it up as a mid-point between a DysonSphere and a planet), in his novel ''Literature/{{Ringworld}}'', but, [[{{Defictionalization}} following feasibility studies,]] have since adopted proper nomenclatural names of [[http://en.wikipedia.org/wiki/Stanford_torus "Stanford Torus"]], and, for the larger version, [[http://en.wikipedia.org/wiki/Bishop_Ring_(habitat) "Bishop Ring"]], while the term "Niven's Ring" remains the designation for [[SciFiWritersHaveNoSenseOfScale colossal megastructures with a star in their center]].

Compare PlanetSpaceship.
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!!Examples

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[[folder:Anime and Manga]]
* The ''Franchise/{{Gundam}}'' franchise helped popularize the O'Neill Cylinder space colony (see below in "Literature"), as well as other designs.
** Actual ring shaped colonies (Known as the "Stanford Torus" or "Island 2" model) are only common in the ''[[Anime/MobileSuitGundamWing Gundam Wing]]'' continuity, though one also shows up in ''[[Anime/MobileSuitGundamUnicorn Gundam Unicorn]]'', which was apparently the first ever built in the UC-verse [[spoiler:and promptly got blown up]].
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[[folder:Comic Books]]
* A ''Defenders'' storyline centered on the [[http://www.marvunapp.com/Appendix/tunnelwo.htm Tunnelworld]].

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[[folder:Film]]
* Possibly the most famous example, the space station from ''Film/TwoThousandOneASpaceOdyssey''.
* The titular space station of ''Film/{{Elysium}}'' appears to be a Stanford Torus.
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[[folder:Literature]]
* Larry Niven's ''Literature/{{Ringworld}}'' is set on a world shaped like a vast ring with a sun at its center. It's made of {{Unobtanium}} called ''scrith'' and is so massive that its geographical features include 1:1-scale maps of several ''planets'' (including Earth). ''These maps are significantly less than 1% of the ring's surface area''. Day and night is created by massive solar panels in spinning in orbit between the sun and the ringworld. [[RamScoop Bussard ramjets]] on the rim of the ringworld keep it centered. The whole thing is reasonably RagnarokProof, which is good, as it's also quite Ragnarok-''prone'': once high-technology civilization there collapses, the absence of available metals means that it can never arise again without outside interference.
* Literature/TheCulture of [[Creator/IainBanks Iain M. Banks]]'s novels builds Ringworld-style Orbitals (but smaller) as housing for many of its citizens. They have a few full size, fits-round-a-star Ringworlds too but they're much rarer, since you can get more useable area by using the same mass to build orbitals so most of the Culture regards them as tacky.
* Creator/ArthurCClarke's ''Rama'' from the series started by ''Literature/RendezvousWithRama'', is a massive cylindrical spacecraft.
* The protagonists of Creator/GregoryBenford's ''Beyond Infinity'' spend a brief time trapped in a Tunnelworld after an encounter with some 4-dimensional aliens. It was a closed loop, so traveling in any direction for a long enough time would return you to your point of origin.
* Gerard O'Neill proposed a real world cylindrical space colony: [[http://en.wikipedia.org/wiki/O%27Neill_cylinder Island Three]].
** The page illustration is a representation of the "Stanford Torus", another design inspired by both O'Neill's work and the classic "wheel-and-hub" space stations.
* Earth in ''Literature/{{Illium}}'' and ''Olympos'' is surrounded by two huge ever moving rings. They are not fun places.
* ''Thistledown'', from Greg Bear's ''Literature/TheWaySeries'', is a hollowed out asteroid containing seven cylindrical chambers separated by bulkheads. The seventh chamber [[spoiler:connects to a cylindrical pocket universe with several million miles of {{terraform}}ed interior.]]
* The {{Anne McCaffrey}} novel ''[[TheShipWho The City Who Fought]]'' takes place entirely on a cylindrical space station.
* The Titans in JohnVarley's Literature/GaeaTrilogy are ''[[spoiler:living]]'' ringworlds.
* In ''ForYourSafety'' the Groupmind builds a Ring around Earth for the humans it had to overthrow in order to save, where they can live in peace under its watchful eye. Though construction time is estimated at 1500 years so the humans have to be put in stasis until then.
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[[folder:Tabletop Games]]
* Sigil from ''DungeonsAndDragons'' Planescape setting is this. It's also a sort of hub that connects to all the other planes of existence.
** There's also Penumbra, the illithid homeworld, which is a full Ringworld. It [[TimeTravelTenseTrouble may or may not exist yet.]]
* In ''TabletopGame/EclipsePhase'' many people following the Fall live in space habitats, many of the bigger ones are toruses or O'neil cylinders. However there's also a number of habitats that don't bother with spinning since basic biomods counter the degeneration from microgravity.
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[[folder:Video Games]]
* ''{{Halo}}'' takes place on a world (Installation 04) resembling Banks' Orbitals at the midpoint between a gas giant and its moon. All of the other Halos appear to orbit gas giants as well.
* ''{{Startopia}}'' has you turn one of these into a profitable space station.
** Several, actually. Apparently, all known races use the same exact design for their space stations, right down to the color scheme.
* ''[[EscapeVelocity EV Nova]]'' has several of these, mostly ring-around-a-planet style. Though one is (for all intents and purposes) THE {{Ringworld}}. (The Polaris use that one for effectively infinite farmland.)
** For bonus ShoutOut points, that ringworld is named Tre'ar ''Helo''nis.
* In ''Franchise/MassEffect'', the Citadel is one of these. In particular, the Presidium is a huge ring with its own biosphere and simulated sky at one end of the space station.
** The Alliance's Arcturus Station is described as a Stanford Torus.
* You can make these in the ''SpaceEmpires'' series. A DysonSphere is better, though.
* Some of the planets in both ''VideoGame/SuperMarioGalaxy'' and ''VideoGame/SuperMarioGalaxy2'', such as the planet in which you fight Megahammer (a HumongousMecha piloted by [[OverlordJr Bowser Jr.]]) on in the latter, actually look like these.
* You can build these in ''VideoGame/StarRuler'', admittedly as a lategame option. They are Capital-H Huge, larger than some planetary orbits.
* ''Videogame/ShoresOfHazeron'' has ancient ringworlds which can be colonized. The ringworlds are almost exactly like those from the ''RingWorld'' novel, with mountains flanking the inner walls, and with shadow squares creating day/night cycles on the surface. Ringworlds have the advantage of being able to carry far more population than a planet, and having 7 different resource zones - if the ore is bad in one zone, it may be high quality in the next one over. Additionally, since the ringworlds are all centered around the sun, and wormholes are always near the sun, any defenses installations on the ringworld will immediately be able to [[AlphaStrike concentrate their fire on anything entering the system]] via wormholes.
* The Torus Aeternal in ''[[VideoGame/{{X}} X3: Terran Confict]]'' is a massive space station ringing Earth's equator. It serves as a docking ring, shipyard, and orbital defense station. In ''X3: Albion Prelude'', [[ApocalypseHow it gets blown up]].

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[[folder:Web Original]]
* The world of Pendor, from ''Literature/TheJournalEntries of Kennet Shardik'', is Niven's {{Ringworld}} with the SerialNumbersFiledOff, because Niven had threatened to sue Elf Sternberg over writing gay BDSM KnownSpace fanfic.
* ''DarwinsSoldiers: Card of Ten'' takes place primarily on one of these.
* So many space habitats in ''OrionsArm''. There are even Banks Orbitals, though system-encompassing rings are impossible to construct.
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