When it comes to the Endless Castle with its Innumerable Doors, keys are power. The more powerful someone is the further away you can hear them coming, clinking with every step. The most important individuals develop a lean to one side and a limp from the weight of their keyrings, which sometimes became bigger around than a beer barrel.
The keys to the Innumerable Doors were as varied as the doors they opened. There were doors whose keys were three dimensional. And some were even stranger; one of the more famous doors required a certain wisp of smoke to open.