The 200,000 KM diameter artificial celestial body of APOSIMZ.
Yet even so, somehow people survive..
And aggressive automatons which appear frequently on the ruins level.
They face the spreading Frame disease.
Fifty centuries ago, the people who lost a war against the core lost their right to reside legitimately in APOSIMZ, and were left behind on the extremely cold surface.
Most of its Volume is its core space, which is covered by a superstructural shell.
The 200,000 KM diameter artificial celestial body of APOSIMZ