Quite possibly my favorite novel of all time, Ringworld is one of the greatest SciFi novels out there. From Wikipedia: In the year 2850, four explorers (two humans and two aliens) are chosen to explore a mysterious "ringworld", an enormous, artificial, ring-shaped structure that surrounds a star. The story is set in an extremely technologically advanced universe, where instant teleportation and indestructible spacecraft hulls are a reality. The protagonist Louis Wu is a retired adventurer who has just celebrated his 200th birthday. Despite his age, he is in near peak physical condition due to advanced medical technology and boosterspice. He spends his birthday hopping ahead of the dateline from party to party across Earth, but secretly he has become bored with his lifestyle. Nessus is a Pierson's Puppeteer, a species with advanced technology whose most notable trait is cowardice. Nessus has been sent to Earth to gather a small team to explore the Ringworld, the existence of which is unknown to most of the species in Known Space. Pierson's Puppeteers have a reputation as manipulators who use other species for jobs that might involve any risk. Speaker-to-Animals is a felinoid Kzin, a ferocious predator species which has unsuccessfully warred with humans in the distant past. He is recruited as the mission's security chief. Finally, Teela Brown is a young human female whose role in the mission is not immediately clear. But Nessus doesn't do anything without a reason, and her usefulness becomes clear as the plot unfolds. When their ship crash lands on the Ringworld, the adventurers must set out to find a way to get back into space. They cross vast distances, witness strangely evolved ecosystems, and interact with some of the Ringworld's varied primitive civilizations. They attempt to discover what caused the Ringworld's inhabitants to lose their technology, and puzzle over who created the Ringworld and why. [image=http://www.btinternet.com/~charles.nightingale/images/Ringworld.jpg] Simply an amazing book.