War of the Roses as a campaign plot. Two noble lines converge somehow, each line thinks it has the rightful claim to the throne. Deciding this long ago was handled by some divine intervention, requiring both houses to come together at some point. They aren't so willing to get together this time. Civil war, or a new king?
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.