Ringworlds are hypothetical space megastructures and massive space habitats in the form of a spinning ring. The centrifugal force generated by this spin generates the force necessary to mimic gravity and hold people and objects on the inner surface. Walls along the edge of the inner surface keep water and gasses from spilling out. Fictional ringworlds could be spaceports, colony ships, or space stations.

If the ringworld surrounds a star, it may also be a Dyson ring. If it orbits a planet, it may be an orbital ring. If either are the case, worldbuilders should note that ringworlds are unstable, and without some way to correct or maintain their location in space, any ringworld will likely drift and eventually collide with whatever is at its’ center.

As with all megastructures, when incorporating ringworlds into your fictional world, consider the purpose for which it was built, who built it, and where the materials for such a vast construction project originated.

Consider the buildings and other places present on the ringworld. If it houses a large population, it may contain areas similar to a large city (consider cyberpunk megacities or planet-wide ecumenopolises as templates). The populations will also need food to sustain itself. This may be accomplished via farms (consider vertical farms and hydroponic farms) or a trade route with another location or planet.

A ringworld is also known as a Niven Ring, after science fiction author Larry Niven who wrote several books describing such a structure.