One of the World Shapes more often found in Science Fiction than in Fantasy, a Ring World Planet is 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 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 Dyson Sphere 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 Larry Niven (who thought it up as a mid-point between a Dyson Sphere and a planet), in his novel Ringworld, but, following feasibility studies, have since adopted proper nomenclatural names of "Stanford Torus," and, for the larger version, "Bishop Ring," while the term "Niven's Ring" remains the designation for colossal megastructures with a star in their center. Compare Planet Spaceship, and the super-trope Centrifugal Gravity.
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Anime and Manga
- The Gundam franchise helped popularize the O'Neill Cylinder space colony (see below in "Literature"), as well as other designs.
- A Defenders storyline centered on the Tunnelworld.
- A Crown Of Stars: Several artificial worlds of the Empire of Avalon are built like this. Shinji and Asuka see several of them as soon as they step through the dimensional portal.
- Possibly the most famous example, the space station from 2001: A Space Odyssey.
- The titular space station of Elysium appears to be a Stanford Torus.
- Most of the changes made to the novel for the film Starship Troopers were execrable, but one of the ones that wasn't was a spaceship docking ring surrounding the entire Earth linked to the surface by space elevators.
- Interstellar: By the end of the movie, humanity managed to leave Earth and starts inhabitating giant space stations that resembles a Stanford Torus.
- Larry Niven's 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. Bussard ramjets on the rim of the ringworld keep it centered. The whole thing is reasonably Ragnarok Proof, 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.
- The Culture of 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.
- Arthur C. Clarke's Rama from the series started by Rendezvous with Rama, is a massive cylindrical spacecraft.
- The protagonists of Gregory Benford'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: 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 Illium and Olympos is surrounded by two huge ever moving rings. They are not fun places.
- Thistledown, from Greg Bear's The Way Series, is a hollowed out asteroid containing seven cylindrical chambers separated by bulkheads. The seventh chamber connects to a cylindrical pocket universe with several million miles of terraformed interior.
- The Titans in John Varley's Gaea Trilogy are living ringworlds.
- In For Your Safety 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.
- Sigil from Dungeons & Dragons 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 may or may not exist yet.
- In Eclipse Phase 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.
- 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. They were originally built by a galactic empire that has since fallen, and a big part of your job is getting them into a usable state.
- 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 Shout-Out points, that ringworld is named Tre'ar Helonis.
- In Mass Effect, 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 Space Empires series. A Dyson Sphere is better, though.
- Some of the planets in both Super Mario Galaxy and Super Mario Galaxy 2, such as the planet in which you fight Megahammer (a Humongous Mecha piloted by Bowser Jr.) on in the latter, actually look like these.
- You can build these in Star Ruler, admittedly as a lategame option. They are Capital-H Huge, larger than some planetary orbits.
- Shores of Hazeron has ancient ringworlds which can be colonized. The ringworlds are almost exactly like those from the Ring World 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 concentrate their fire on anything entering the system via wormholes.
- The Torus Aeternal in 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, it gets blown up.
- The Teladi Union's space station in X Rebirth has a centrifugal habitation ring that is over a dozen kilometers wide. The ring has an artificial atmosphere contained by energy shields, and alternates between manufacturing sectors and park-like habitation sectors.
- In Stellaris, Fallen Empires sometimes have ringworlds build around stars, and one will occasionally find heavily-guarded ring worlds serving as nature preserves. The building methods in either case are long since lost.
- The world of Pendor, from The Journal Entries of Kennet Shardik, is Niven's Ringworld with the Serial Numbers Filed Off, because Niven had threatened to sue Elf Sternberg over writing gay BDSM Known Space fanfic.
- Darwin's Soldiers: Card of Ten takes place primarily on one of these.
- So many space habitats in Orion's Arm. There are even Banks Orbitals, though system-encompassing rings are impossible to construct.
- https://www.youtube.com/watch?v=fJvbO_rR07g Life on a Donut Planet.