Megastructures Ringworld 2

A Ringworld is an artificial ring in space large enough to maintain an atmosphere and habitable land. The ring spins to create g-forces, and inner walls could be used to hold in the atmosphere. “Stellar Scale” rings could have a radius roughly equal to the radius of the Earth's orbit around the sun, and could in fact have a sun at its centroid.

Part of the Megastructures book project, to be released late 2021 / early 2022: http://www.neilblevins.com/books/megastructures/megastructures.htm