Free-flying catamaran cities cruise the bottomless skies of the gas torus called the Mashveya. The twin cylinders, known as the boroughs, each consist of a stationary outer shell surrounding a handful of flimsy inner shells that rotate at increasingly higher speeds. Driven by diesel locomotive engines, the aerocity’s innermost, inhabited cylinders both rotate in opposite directions to one another, canceling out each others’ torque on the connecting bar between them, allowing them to maintain a comfortable 0.4 gees of centrifugal gravity. Propeller engines and not-pictured aerodynamic surfaces provide maneuver thrust and attitude control.

Multiple aerocities often congregate into a greater metropolis. Each catamaran can support about 40,000 Capuans in self-sufficient agriculture mode, and about 100,000 at full urbanization. The catamarans shown here are flying relatively far apart, above the Windwoods of a forested asteroid.

Credit to Alan Rominger at the Gravitational Space Balloons project for many of the concepts employed here, and for help in understanding how the cylinders spin up.

Check out my content creation tumblr if you're interested in the worldbuilding behind this design.