Many dabble with the Occult at some stage. Those travelled and wise to the world know that there is a darker, unknown side to life. Necromancers toy on the fringes of the Occult energies to fuel their art, and those of zeal and religious fervor occasionally succumb to the darker side of their faith. Demons. Devils. Infernal realms. The Weird and unnatural. Elder beings you dare not awaken. All are the domain of the occult. Come; stop wading in the shallows and plunge into the depths! Fall to the darker art and discover what the Occult Brotherhood has to offer.
The Yugzhee, or "hedgehog-people", guard a great, secret treasure inside their giant burrowed lair. The mysterious Wall of Keys, a 12'x10', foot-thick, cold-iron, "wall", upon which, on iron hooks, hang 100 ornate iron keys of all shapes and sizes. Each key opens some heretofore un-openable barrier, door, or gate, in the particular game world of choice.
The PCs have come upon a great boon, except for the fact that the keys cease to function properly if separated from the iron wall for more than a few minutes. Higher level characters will be able to figure out how to take the wall "with them" via magic. Lower level characters will have to get creative.