In all the stories where adventurers find a map to a lost treasure, buy it from an adventure in a tavern or any of the other ways they come upon such things, the Mystery is: Where do all these maps to lost things come from? If there is a map to a thing then how comes it is still considered as lost? The answer lies in the ancient and equally mysterious figure only known as The Cartographer. From the very beginning, the Arbiters of the Universe assigned him to see to it that all lost things be found, a place for everything and everything in it's place so he has been tirelessly creating maps to any and all things that have slipped from living memory. He has been doing this so long his own beard has started to become parchment.
His "shop" appears wherever there is a spare space that no one is paying attention to and once it is there it has always been there, full shelves of old maps and parchments that seemingly go on forever, seemingly leaking these maps into the world. And when his shop is no longer needed, it disappears and was never there to begin with.
He has a ... cantankerous relationship with Amos since Amos was one of the few to actually seek out where these treasure maps come from and now knows when he wants something, the shop will always be there even if The Cartographer wishes it wasn't since, to get his way, Amos is always threatening to spill ink over his work or set fire to his shop... It's part of the banter they do. In return, The Cartographer always creates maps to places full of traps, hoping one will stop Amos from coming back, but alas they never do.