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.
The World is actually a number of continents surrounded by oceans, which are in turn surrounded by mountains. The oceans rush off the edge of the plateau on which the World sits into the Outside...