<p>Welcome to Ringworld an intermediate step between Dyson Spheres and planets. Ninety-three million miles in radius—the equivalent of one Earth orbit or 600 miles long—1000 meters thick and much sturdier than a Dyson sphere.</p><p>What other advantages are there to this world? The gravitational force created by a rotation on its axis of 770 miles per second means no need for a roof. Walls 1000 miles high at each rim will let in the sun and prevent much air from escaping.</p>
