Rendezvous With Rama by Arthur C. Clarke

"The enigmatic object christened Rama was detected while still outside the orbit of Jupiter. A first radar contact at such a distance was unprecedented, indicating that Rama was of exceptional size. As it raced through the Solar System, it became apparent that Rama was a cylinder so geometrically perfect that it might have been turned on a gigantic lathe. Mankind was about to receive its first visitor from the stars"--Back cover.