Ringworld (1970) by Larry Niven is a science fiction book that won the Hugo and Nebula awards.
The book is the tale of a journey by two humans a Kzin (a large cat type humanoid) and Nessus who is one of a race of Pierson’s Puppeteers that are three-legged highly intelligent beings. The crew take off in a fast space ship the edges of known space to explore a vast ring that surrounds a star. The ring is a huge construction that provides a vast living area. The ring has fallen into barbarism as the civilisation there collapsed.
The details of the story are excellent. The characters are a little thin though. The book also sags somewhat in parts. Still, it is not hard to see why the book is regarded as a science fiction classic.