Rendezvous with Rama is widely acclaimed as Arthur C. Clarke's best book, and it definitely deserves much of the praise it's gotten. That said, the book isn't perfect, particularly when it comes to the characters.
Rendezvous with Rama starts when an large, cylindrical object is detected hurtling towards the sun. The object is named "Rama" after the Hindu god. The United Planets sends the solar survey vessel Endeavour under the command of Commander Bill Norton to investigate. The rest of the book focuses on the crew's exploration of the alien artifact.