The People of the pocket realm of Brocschtal are simple folk who live as they have for thousands of years. Farming the land, raising sheep, getting in the occasional brawl. And fighting off the infernal attacks of ghouls.
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.