The Dark Citadel is an immense stone construction in Hell, with vast courtyards and spacious corridors. In addition to the Unholy Cathedral this is one of the most interesting sites in Hell for scientific demonology, as it offers another glimpse into the mysterious nature of the demons. A secret passageway into the lower levels of this complex leads to what appears to be a full demonic library complete with thousands upon thousands of books. This surprising discovery is the first recorded indication of a literary culture among the demons, or indeed any type of high culture beyond the bizarre, indecipherable rituals commonly observed.
Interestingly, the library appears to be staffed almost solely by demons of the Baron family; Hell Knights and Barons of Hell, as well as humans under demonic possession. The implications of this are far-reaching, possibly indicating that humans may have uses in the social structure of Hell other than their well-known role in abundant ritual torture. Furthermore, if the Barons are the actual keepers of the library, they must be vastly more intelligent than what their animalistic nature would have us believe at first sight.
One can only wonder in fascination as to what the contents of the various demonic tomes hidden in this arcane library are, and how they might be used by their keepers. Some indication of their unnatural practices is betrayed by the fact that while the books themselves appear well kept, piles of rotting flesh hang from the ceiling and litter the hallways of this unholy library in another grotesque display of the alien customs of Hell's minions.