Larry Niven's Ringworld is one of the great hard SF novels. Here's the setup:
And have many adventures along the way! The Ringworld really is a mind-blowing concept and very well-developed in the book. As for what or who the Kzin and Puppeteers are....well, you'll just have to read the book. These are creatures first introduced in Niven's extensive Known Space future history, pretty much all of which is worth reading. As for Niven's later stuff I find it hit or miss, particularly that written with other authors. But Ringworld is the pure quill. Highly recommended.On planet Earth in 2850 AD, Louis Gridley Wu is celebrating his 200th birthday. Despite his age, Louis is in perfect physical condition (due to the longevity drug boosterspice). He has once again become bored with human society and is thinking about taking one of his periodic sabbaticals, alone in a spaceship far away from other people. He meets Nessus, a Pierson's puppeteer, who offers him a mysterious job with almost no details. Intrigued, Louis eventually accepts. Speaker-to-Animals (Speaker), who is a Kzin, and Teela Brown, a young human woman who becomes Louis' lover, also join the crew.They first go to the puppeteer home world, where they learn that the expedition's goal is to investigate the Ringworld to see if it poses any threat. The Ringworld is a gigantic artificial ring about one million miles (1,600,000 km) wide and approximately the diameter of Earth's orbit (which makes it about 600,000,000 miles or 950,000,000 km in circumference), encircling a sunlike star. It rotates to provide artificial gravity 99.2% as strong as Earth's from centrifugal force. The Ringworld has a habitable, flat inner surface (equivalent in area to approximately three million Earths), a breathable atmosphere and a temperature optimum for humans. Night is provided by an inner ring of shadow squares which are connected to each other by thin, ultra-strong wire. When the crew completes their mission, they will be given the starship in which they will travel to the Ringworld; it is far faster than any possessed by humans or Kzinti.When they reach the vicinity of the Ringworld, they are unable to contact anyone, and their ship, the Lying Bastard, is disabled by the Ringworld's automated meteoroid-defense system. The severely damaged vessel collides with a strand of shadow-square wire and crash-lands near a huge mountain. Many of the ship's systems survive intact, including the faster-than-light hyperdrive, but the normal drive is destroyed, leaving them unable to launch back into space to use the hyperdrive. They set out to find a way to get home.