There are ruins, scattered about the world, and all are sealed with unbreakable locks.
When all of these locks suddenly open, what emerges?
A cave with weapons sunken into the walls, blades sticking out of the floor and ceiling, and so on. Possibly, any weapon used in it could be torn out of the hand and sink into the stone.
Small identical wooden or metal discs with a strange pattern engraved upon them (do not appear to be coinage). The discs can be found all over the continent; a farmer typically overturns several dozen when ploughing a field. Though they are unnaturally hard to break, they have no known use and are widely used as good-luck charms: almost all households would have them on the doors and on mantle pieces; many people carry one or more on them, bound on to a belt, necklace or sewn on to their clothes.