Ringworld is an award winning Science Fiction book by Larry Niven and also a ring-shaped structure encircling and orbiting a star at a safe distance, described in that book.
Larry Niven's Hugo, Nebula, and Locus award-winning, novel Ringworld (first published in 1970) depicts an exploration of a ring shaped structure that encircles and orbits a star, also called a Ringworld. This term may also refer to other literary works that discuss the phenomenon in Larry Niven's book.
The Ringworld is an artificial ring about one million miles wide and approximately the diameter of Earth's orbit encircling a star. It rotates, providing an artificial gravity and has a habitable flat inner surface. The Ringworld could be regarded as a thin, rotating slice of a Dyson sphere, with which it shares a number of characteristics.
Wikipedia has more information about both the novel and the world concept.
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