"The magic's what operates the door," says Varric. "Some mage or other enchanted a perfectly ordinary tavern door so that from time to time, when people somewhere else are minding their own business and pass through a door in their own ... world, or realm, or whatever you want to call it... the door they open comes to this place instead. They walk in here, they see all kinds of people they don't know from all kinds of places that might or might not exist where they come from, they develop headaches trying to figure it out. Then there's usually the drinks, the first of which is free, while they try to figure it out some more. Eventually they go home and then the headaches start again, because they return to the moment they left."