Gently used, from non-smoking environment.

The Ringworld Engineers is a 1979 science fiction novel by American writer Larry Niven. It is the first sequel to Niven's Ringworld.

Twenty years after Louis Wu discovered Ringworld, he and Speaker-to-Animals are going back as captives of the Hindmost who hopes to regain his place as puppeteer leader by impressing the other puppeteers with Ringworld treasures. But when they arrive, they discover that Ringworld in no longer stable and will destroy itself within months.  To survive, they must locate the control center of the engineers who built the planet.