Medrengard

Medrengard is Perturabo's daemon world in the Eye, a fortress-planet under a black star that drinks light. Warsmiths raise kilometre-spires as docks, slaves die in the foundries of Pyriphon, and the primarch sits in the Kolasikon on an onyx isle in a lava lake. The Iron Warriors have fought each other here as often as they have fought anyone else.