A new place is being built, a world of huge dimensions, encompassing millions of miles, stronger than any planet before it. There is gravity, and with high walls and its proximity to the sun, a livable new planet that is three million times the area of the Earth can be formed. We can start again!

Ringworld, the most celebrated work in Niven’s “Known Space” sequence, posited a vast body of matter — enough for an entire solar system — spinning around a sun in the form of a single giant artifact of unknown origin: a continuous million-mile-wide ribbon provided with oceans, atmosphere, and vast flat projections (life-size “maps”) of Earth and other inhabited planets. The present book takes up the puzzle some 20 years after Louis Wu’s escape from the Ringworld. Kidnapped by the mate of Nessus, their two-headed alien companion of the previous voyage, Louis and his catlike ally Chmeee are transported to the Ringworld — now spinning dangerously off-center — in an attempt to discover the cause of the aberrant rotation before the world grazes its sun. Searching for clues to the design of the structure’s long-vanished original engineers, they encounter various hominid and other races before finding the barely feasible, wholly appalling solution hidden beneath the “Map of Mars.” Niven, a longstanding favorite with “hard” SF buffs, commands an impressive vein of invention, but his plotting here is limp and threadbare; the idea was more striking the first time around. Nominated for Hugo and Locus awards for best novel in 1981

An honored SF writer returns to his best-known creation: the artificial world, built far from Earth by aliens over a half million years ago, in the form of a ring 600 million miles in diameter, hosting an astonishing multitude of inhabitants and cultures. This third fictional voyage to the Ringworld (after Ringworld, 1970, which won both the Hugo and the Nebula for best SF novel of that year, and Ringworld Engineers, 1980) offers two stories crowded into one. A motley array of hominid inhabitants are seeking to defeat a plague of vampires. Meanwhile, returning hero Louis Wu is battling what effectively is a plague of Protectors (superbeings common to many Niven novels) whose rivalries threaten Ringworld’s existence. The battle against the vampires is the more exciting of the two stories, filled with action, scenes of the Ringworld and explorations of ritualistic interspecies sex. Wu’s pursuit of the Protectors displays Niven;s deft hand at portraying aliens, but the dialogue that fills in the backstory slows the narrative. Niven still ranks near the top of the SF field, but this outing is likely to satisfy determined Ringworld fans more than other readers

Ringworld’s Children returns series protagonist Louis Wu to the titular world. Louis and his friend The Hindmost, an alien of the Pierson’s puppeteer race, are prisoners of the Ghoul protector Tunesmith, a Ringworld native, who is deliberately provoking the warships that surround his world. All the star-faring races of Known Space have sent warships to the Ringworld, and they are already at the brink of war. If fighting breaks out, the near-indestructible Ringworld will be destroyed: dissolved by antimatter weapons. The Ringworld series is so complex and ambitious that Ringworld’s Children opens with a glossary and a cast of characters, inclusions that even many Known Space fans will need. Newcomers to Niven’s artificial planet should start with Ringworld