Avantis, the Gem of Voidspace
Avantis is the city of a 1000 races. All who travel between the stars know of Avantis and have bases set up within the city. Avantis is a giant asteroid, which is covered from edge to edge with a living city. It is protected and enclosed by the Arches, ancient amarnium structures which hold out the void of space and keep the air and gravity in. No one knows who built Avantis or the Arches, but now all benefit. Avantis is the only place where the Eldar-Illarth war is put on hold, and both races share the same ground.
The gravity field of Avantis splits it in half, the top half is the home of the Guild Council, the merchant quarter and the docks. The Underside is the slums and military base.
The city is ruled by guilds, and the top 10 guilds sit on the council.