Ringworld

Ringworld is a 1970 science fiction novel by the American author Larry Niven and the first of four novels set on the structure of the same name.

The Ringworld is the book's central invention: an artificial ring six hundred million miles in circumference encircling a star, with a habitable inner surface. The remainder of the sequence consists of The Ringworld Engineers in 1980, The Ringworld Throne in 1996 and Ringworld's Children in 2004, and the core series was extended by side series set in the same universe, including the Man-Kzin Wars and the Fleet of Worlds books written with Edward M. Lerner. The ring is a habitat rather than a ship, which is why the novel can spend its length on the difficulty of understanding a place that was built to be lived in.

The novel belongs to Niven's broader Known Space setting, so it shares a background with a large body of other stories while remaining readable on its own. Its reputation rests on the engineering premise and on the problem the expedition has in comprehending a structure of that scale, which is why it is usually grouped with the hard science fiction of its period.