This adult science fiction series is set in a future where humanity has joined a galactic community of species, and follows an expedition to investigate a vast artificial ring structure built around a distant star — a construction of almost incomprehensible scale that turns out to hold many more mysteries than the crew anticipated. The series is a landmark of hard science fiction world-building, centered on the concept of the Ringworld itself and the civilizations that built and inhabit it.
A mixed team of two humans, a catlike alien, and a two-headed alien from a species that evolved on luck sets out to explore the most astonishing structure in the known galaxy: the Ringworld, an enormous artificial band encircling a star with a surface area of millions of Earths. When they crash-land on its inner surface, the group must survive and unravel the mystery of why it was built and where its builders went. A landmark of hard science fiction worldbuilding.