Like many Earth-based demonic hives, this site may have originally been some sort of a human settlement. As a result of the failure of the Plutonia Experiment however, it was corrupted by the forces of Hell, turned into a gruesome fortress of stone, flesh and metal.
The compound was occupied by many powerful demons, including Arch-Viles and Barons of Hell involved in bizarre Hellish rituals, as well as a Spider Mastermind who is assumed to be a type of a "commander" of this facility. From this, it may be postulated the site was of some importance to the demonic invasion force.
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Bizarre rituals performed on still alive soldiers.