The Ringworld Engineers by Larry Niven

The plot of the novel centers on the instability of the Ringworld. The recently-deposed Hindmost, leader of the Puppeteers, abducts the human Louis Wu (who has become a wirehead) and kzinti Chmeee (previously known as “Speaker-to-Animals”). Both were part of the Ringworld exploration in the first novel. The Hindmost hopes to acquire Ringworld technology that he hopes will help him reacquire his position as leader. In the course of the novel, Louis and Chmeee set forth on an exploration of the Ringworld in order to learn where the creators of the Ringworld may have built a control or repair system. In their travels they meet a number of the hominid species that have evolved on the Ringworld. They also learn more about the “maps” of various known space worlds that are located in one of the Ringworld’s great oceans. These full-size maps include, among others, Kzin, Earth, and Mars. It is on the Map of Mars that the party finds the Ringworld control room, located in a vast maze of rooms contained in the hollow space under the map. In order to create the rarefied atmosphere on Mars, the Map of Mars was built to an altitude 20 miles above the main Ringworld surface creating a 1,120,000,000 cubic mile cavity. The Control Room contains living space for thousands of Pak Protectors, as well as space to grow the “Tree-of-Life” plants to support this many Protectors. Other rooms in the cavity support such features as the “Meteor Defense System”, which uses the superconductor grid embedded in the scrith foundation material to manipulate the magnetic field of the Ringworld’s sun to create a solar flare; it uses this to generate a powerful gas laser, which is capable of destroying everything in its path. In the course of finding the control room and saving the Ringworld, the party learns what became of Teela Brown, who had been left behind after the exploration twenty years earlier led by the Puppeteer, Nessus.