The City of Immortals' dungeon lay two hundred meters beneath the grand Gothic tower of the Ministry of Internal Affairs. Originally built by the Brotherhood of the Shield at least five hundred years ago, it was designed to imprison dangerous criminals and store hazardous equipment. Thick Vibranium alloy and granite sealed the dungeon off from the outside world. Compared to this dungeon, the vaults of every bank in the world were as fragile as glass windows that could be shattered with a casual tap of the knuckles.
After taking over, Salomon personally designed and rebuilt the place. Using powerful engineering machinery, he widened and reinforced it further, turning it into a dungeon beneath a dungeon—though he himself was reluctant to admit it, Maya Hansen, the City of Immortals' first official employee, had once been fortunate enough to witness her boss holding a shovel, casting a spell on a vast rock wall to turn it into earth, then digging away with abandon. At the time, Salomon had no resources, so he could only do many things himself. He even tried to find amusement in hardship, calling it "another great feat after Summoning the Seventy-Two Pillars of Demons to build the temple."
The renovated dungeon was as intricate as a spiderweb. One had to know the proper route and pass layer after layer of inspections to make it through the rooms housing security personnel and find the platform leading into the dungeon's core without getting lost. Yet reaching the core level did not mean it was over. Every passageway, regardless of length, was fitted with Heavy Bolter Machine Guns. Independently operating low-level artificial intelligences controlled those terrifying weapons, and anyone who did not belong there would face a dreadful Metal Storm.
Beyond that, alchemical war machines, restricted only by the Praetorian Guard