The city of Vanaaris located in Avernus. The city floats in the sky above the surface of Avernus, resting on top of a floating land mass that was at one time one of Baator’s moons. The small moon was a stage for a battle in the Blood War that literally cut the land mass in half and brought it out of orbit so that it floats a mere four miles above Avernus’ surface. Now a half circle, the top flat of the ‘moon’ houses the city.
The climate of Vanaaris is much cooler than that of the surface of Avernus and thus typically houses those from the mortal realm that would serve the fiendish populations of Baator (such as Warlocks). The buildings in Vanaaris take on many different architectures as they were built by multiple different races from different Cosmologies. However, the bulk of the buildings are made out of the red rocks and rubble that were left from the great battle that once took place, including the bones and gore from demons that were slain.
The city itself has become somewhat of a “docking station” for those who would enter Baator, servants, damned, and slaves alike. Many slaves that are forced to stay in the city, are typically there for cleanup duty to continue removing the remainder of the battle that took place centuries ago or to build on to the city.
Below the city are the catacombs of Vanaaris, dug into what remained of the moon to house the bones of fallen devils (and probably some demons). It is also a place where many of the citizens of Avernus bring their dead.
If you were took look up from Avernus’s surface at the city, you would see water falls of black liquid dumping down the edges of the half moon, this black liquid has served as a source of transportation within the city as black water canals grid through the city like a maze. The liquid itself is highly toxic and seems to flow without end from an unknown source. However, when the black liquid touches Avernus’ surface it immediately evaporates into a putrid black steam that rises up underneath the city.