The Grumbles
This merchant ‘district’ can be found in any reasonably magical fantasy setting; it typically operates inside a single large building. The more decrepit, the better: the wooden beams should be scarred and worm-ridden, the metal nails must be staining the walls black, and the roof — well, nobody in the Grumbles ever actually sees the roof from the inside, but it should be about to fall apart, or possibly over. Oh, and the building should be on the local riverfront. Easier to get shipments in and out that way.