Larry Niven wrote a lot of books set in "Known Space," and I read pretty much all of them when I was in my teens. I was curious to see what Ringworld looked like more than 30 years later.
The premise is fairly simple: a ring of material spins around a star, about one Astronomical Unit (ie. the orbit of the Earth) in radius. The ring is a million miles wide, and has an edge a thousand miles high to hold in the atmosphere that's held down by centrifugal force. The surface area is three million times that of the Earth.
But that isn't where the adventure starts: it starts with Louis Wu, 200 years old, being approached by a Pierson's Puppeteer (a race that had left Known Space 200 years previously). Eventually, he, the Puppeteer, a Kzinti called "Speaker to Animals," and another human - a young woman called Teela Brown - head for the Ringworld the Puppeteers have discovered to investigate.
In light of modern technology there are some blatant failures: I particularly remember them making sketches of maps they couldn't remove, whereas any of us today would snap a photo on our cellphone - but in 1970, Niven hadn't anticipated our favourite do-anything device. There are some problems like this with the novel, but for the most part his speculations about aliens and technology are fascinating, and the story is very well constructed. Still a very enjoyable book.