Ringworld
Larry Niven
 The novel opens in 2850. Louis Gridley Wu is celebrating his 200th birthday. Despite his age, Louis is in perfect physical condition but is bored. He has experienced life thoroughly, and is thinking of taking a trip to and beyond the reaches of Known Space, all alone in a spaceship for a year or more. He is confronted by Nessus, a Pierson's Puppeteer, and offered one of three open positions on an exploration voyage beyond Known Space. Speaker-to-Animals (Speaker), who is a Kzin, and Teela Brown, a young human woman, also join the voyage. They first travel to the Puppeteer home world, where they learn that the expedition's goal is to explore a ringworld: an artificial ring about one million miles wide and approximately the diameter of Earth's orbit (which makes it about 600 million miles in circumference), encircling a Sol-type star. It rotates, providing artificial gravity that is 99.2% as strong as Earth's gravity through the action of centrifugal force. The ringworld has a habitable flat inner surface equivalent in area to approximately three million Earth-sized planets. Night is provided by an inner ring of shadow squares which are connected to each other by thin, ultra-strong wire (shadow square wire). None of the crew's attempts at contacting the Ringworld succeed, and their ship is disabled by its automated meteor defense system. The severely damaged vessel collides with a strand of shadow-square wire and crash-lands on the Ringworld near a huge mountain. The ship's defences keep the crew compartment and many of the ship's systems intact, including the faster-than-light drive (hyperdrive), but the normal drive is destroyed, leaving them unable to launch back into space to use the hyperdrive. The team now has to set out to find a way to get back into space, as well as fulfilling their original mission – learning more about the Ringworld. Using their flycycles, they try to reach the rim of the ring, where they hope to find some technology that will help them. It will take them months to cross the vast distance. When Teela develops "Plateau trance", they find themselves forced to land. On the ground, they encounter apparently human Ringworld natives. The natives, who are living primitively in the crumbling ruins of a once advanced city, think that the crew are the Engineers of the Ring, whom they revere as gods. The crew is attacked when they commit a "blasphemy". They continue their journey during which Nessus is forced to reveal some Puppeteer secrets: they have performed indirect "breeding experiments" on both humans (breeding for luck) and kzin (breeding for less aggressiveness). The resulting hostility forces Nessus to abandon the other three and follow them at a safe distance. They encounter a city and, in a floating building, they find a map of the Ringworld and videos of its past civilization. In a giant storm, caused by air escaping through a hole in the Ring floor due to meteor impact, Teela is blown away in an unknown direction. While searching for her in a ruined city Louis' and Speaker's flycycles are caught by an automatic police station designed to catch traffic offenders. They are trapped in a prison in the basement of the police station. Nessus arrives, entering the station to help his team. In the station they meet Halrloprillalar Hotrufan ("Prill"), a former crew member of a spaceship used for trade between the Ringworld and other inhabited worlds. Her spaceship was stranded on the Ringworld when the landing mechanism failed. She relates what she learned of the downfall of the Ringworld's civilization: A mold that breaks down superconductors was introduced by a visiting spaceship. Without its superconductive technology, civilization fell. Teela reaches the police station, accompanied by her new lover, a native "hero" called Seeker who helped her survive. Based on his studies of an ancient Ringworld map, Louis devises a plan to escape. The four explorers, with Seeker and Prill, use the floating police station as a vehicle to travel back to the explorers' crashed ship. Along the way, Teela and Seeker choose to remain behind, to inhabit a flying castle and remain on Ringworld. The remaining explorers and Prill collect one end of the shadow square wire that was dislodged when the ship crashed, dragging the wire behind them as they travel. Reaching the wreck, Louis threads the shadow wire through the crashed ship and uses it to tether the ship to the police station, and then continues to pull the wire onward, up to the summit of "Fist-of-God", the enormous mountain near their crash site. The massive mountain does not appear on a map of the original Ringworld, leading Louis to conclude that it is in fact the result of a meteor impact with the underside of the ring, which pushed the "mountain" up from the ring floor and broke through. The top of the mountain, above the edge of the Ring's atmosphere, is therefore a passage to the underside of the Ringworld and freedom. Louis drives the police station over the edge of the crater. Because the Ringworld spins fast enough to provide gravity, once the police station and ship are on the underside, centrifugal force pushes them outward from the ring into open space. The crew can then use the ship's faster-than-light drive to get home. The book concludes with Louis and Speaker discussing returning to the Ringworld.