A massive space station that much of humanity resides on. It has a population of 3 trillion due to its expandability. Many different civilizations live in and on the station- some of the lower ones unaware of the existence of other civilizations outside of legends. Others are less isolated but have little knowledge of the overall political landscape on the surface.
The Station is large enough to hold its own atmosphere, so you can safely stand outside on the upper levels without extra oxygen.
Expandability
The progress of the station would not be possible without Matter Converters. These are devices which can convert the mass of an object into another form. They do have limits on what can be obtained from them however, so there are many valuable materials such as gold that still need to be to be mined from asteroids or uninhabitable planets.
Legends
One legend is that the station was built on top of the original Rip Drive Ship.