Here's one for the hard science fiction lovers. Imagine a world created by making a ring of material around a sun. Gravity comes from the rotation of the ring, and night from platforms in a tighter orbit around the sun. Think of having three million times the space of Earth. That's the Ringworld.

Two humans, a Kzin and a Pierson's Puppeteer are sent to explore the mysterious Ringworld, which the Puppeteers have discovered, but as a determinedly cowardly race refuse to explore on their own. The Puppeteer with them, in fact, is considered insane by others of his own race.

Teela, the human female, can be a somewhat absurd character. She is exceptionally lucky, and it is for that which she was chosen for the mission. But this also makes her incredibly stupid about danger. Of course, for her it all works out in the end so it doesn't matter so much that she doesn't really understand danger, pain (either emotional or physical), and so forth.

Honestly, in this case I enjoyed the concepts of the book much more than the characters. I really didn't sympathize with any of them, although Nessus, the Puppeteer, was often interesting. Not only is the Ringworld well imagined, but so is protecting it from damage, what happens when it is damaged and how the Ringworld would appear to its inhabitants.