Ringworld (1970) by Larry Niven, is the first of a series of stories – including prequels and sequels – set in a version of the universe called the Known Space. It features as backdrop an artificial structure of 600 million miles in circumference around a star, the Ringworld. The giant ring has a habitable inner surface, almost Earthian gravity and regular cycles of day and night. Original and entertaining, the book soon became a classic and a few SF authors have since then used some types of circular superstructures for their own stories. Ringworld won the Nebula Award, the Hugo Award and the Locus Award.
