Welcome to Ringworld, an intermediate step between Dyson Spheres and planets. The gravitational force created by a rotation on its axis of 770 miles per second means no need for a roof. Walls 1,000 miles high at each rim will let in the sun and prevent much air from escaping. Larry Niven's novel, Ringworld, is the winner of the 1970 Hugo Award for Best Novel, the 1970 Nebula Award for Best Novel, and the 1972 Ditmars, an Australian award for Best International Science Fiction.

The Eternals, the ruling class of the Future, had the power of life and death not only over every human being but over the very centuries into which they were born. Past, Present, and Future could be created or destroyed at will. You had to be special to become an Eternal. Andrew Harlan was special. Until he committed the one unforgivable sin - falling in love. Eternals weren’t supposed to have feelings. But Andrew could not deny the sensations that were struggling within him. He knew he could not keep this secret forever. And so he began to plan his escape.

The year is 2312. Scientific and technological advances have opened gateways to an extraordinary future. Earth is no longer humanity's only home; new habitats have been created throughout the solar system on moons, planets, and in between. But in this year, 2312, a sequence of events will force humanity to confront its past, its present, and its future. The first event takes place on Mercury, on the city of Terminator, itself a miracle of engineering on an unprecedented scale. It is an unexpected death, but one that might have been foreseen....

Six million years ago, at the very dawn of the starfaring era, Abigail Gentian fractured herself into a thousand male and female clones: the shatterlings. Sent out into the galaxy, these shatterlings have stood aloof as they document the rise and fall of countless human empires. They meet every 200,000 years to exchange news and memories of their travels with their siblings.

In the 1800s, a sailing ship crashes off the coast of Norway. In the 1900s, a Zepellin explores an icy canyon in Antarctica. In the far future, a spaceship sets out for an alien artifact. Each excursion goes horribly wrong. And on every journey, Dr. Silas Coade is the physician, but only Silas seems to realize that these events keep repeating themselves. And it's up to him to figure out why and how. And how to stop it all from happening again.