Ringworld is a 1970 science fiction novel by Larry Niven, set in his Known Space universe and considered a classic of science fiction literature. It is followed by three sequels and four prequels, and ties into numerous other books set in Known Space.
The novel opens in the year 2850 A.D. on Earth. 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.
Ringworld Prequel series (Larry Niven and Edward M. Lerner?)
Ringworld (Larry Niven)
More: The Ringworld,