The Pandemonium Club is an organization of mundanes with a deep interest in the Shadow World. It is said to be a rather old organization of mundanes who have interested themselves in the magical arts where, at their meetings, they do spells and try to summon up demons and spirits. Other members are simply enthusiasts who use their money and influence to purchase knowledge of the unknown world. They are powerful in the Downworld, their members being rich and important figures in mundane society.
Its symbol was a double ouroboros, two serpents biting each other's tails to form a circle, symbolizing the end of the world and the beginning.
In the 1800s, they were headed by the Magister, whose main purpose then was to destroy the Nephilim. With the Dark Sisters at his disposal, they supervised a set of secret gambling dens frequented by Downworlders. They existed to lure mundanes in and trick them into losing all their money in magical games, then, when the mundanes fell into debt, they would extort the money back at ruinous rates. They ran some other businesses as well, most unsavory ones, such as brothels.
In modern times, the Pandemonium Enterprises, now possibly more involved in the Downworld, is a company that still continues to cater to the desires of their wealthy patrons. A Caroline Connor is assigned in providing entertainment for their customers in a nautical environment, particularly an exclusive cruise, wherein a gourmet meal is served on a yacht with a view of the magical denizens found in the New York Harbor—nixies, kelpies, mermaids, and various other water sprites. Connor introduced herself as the CFO and marketing VP of Sigblad Enterprises; it is unclear if this was a pseudonym for the organization or an entirely separate one employed by the Club.
- Most of the mundanes who attended the club events were masked or disguised at club events. Some of its more notable Downworlder attendees included Magnus Bane, Camille Belcourt, Ragnor Fell, and Alexei de Quincey.
- Mortmain has mentioned certain magical innovations discussed and shown in Pandemonium meetings which have since come into fruition, namely: "a silver ring [created by a warlock] that could transport the wearer to another location whenever he twisted one around his finger," rings which both Mortmain and Valentine Morgenstern came to possess at one point; "a doorway that could bring you anywhere in the world"—the Portal, though whether the aforementioned doorway is some other warlock's vision or prototype or if it was something pitched by the second half of the Portal's creator, Magnus, is unknown; and "I've seen men brought back from the brink of death", referring to the practice of necromancy that is known to have been occurring for a long time.