The Wasting Tower
This macro-titanic edifice is the center of power for all daemonkind. The towers exact origins are unknown, although the venerable maskim are said to have been alive during the towers construction and whisper that sinistral overgods summoned a mega-being from beyond reality in the first war against the angels. However the mindless entity could not be controlled and ran amok. Forced into battling the creature, in a conflict where even overgods met their end, the monstrosity was eventually laid low. Over time the carcass of the great beast decayed and rotted, forever blighting the plane of Hades. Only the bones now remain, with the wasting tower being created from the creatures spine.
Over the eons the tower has inspired daemonic architects and broken the backs of the billions of slaves that have laboured upon it. The tower reputedly has some ten thousand levels, with roughly half above ground and half below.