A stepped habitat, on nine levels, all revolved at the same speed, the outer tiers possessed greater apparent gravity than those nearer the centre.
The levels are sectioned into compartments up to hundreds of kilometres long and filled with atmospheres of different types and held at different temperatures, while it can mimic the conditions on a hundred different worlds for a hundred different intelligent species.
It has existed for seven thousand years by the time described in Excession.
Its original builders are unknown; they were believed to have Sublimed shortly after building it. They have left behind a species to run and maintain the place, small spheres covered with long articulated spines, between half a metre and two metres.