A mega ringworld. Larger than normal ones. A machine left behind by a empire named the Juran empire. Now only know as a forgotten empire. Since this 100,000s of years have past.
10000s of earth's could fit inside the ring? Many of the descendants turned into tribes farmer empires.
All lost the ability to transport to other star systems becoming locked to the ring.
Alien races To humans were love to this world, many making their own empires, some creating their own unique features to the ring. ..