Medieval Finns believed stone age artifacts were magical. The millennia-old knapped stone tools sometimes turned up by their plows could, they thought, ward off evil. Medieval Finns buried these tools in the foundations of their walls and hearths to guard their homes. There’s something very cool about stone arrowheads and adzes as wards, whether they were made by your long-forgotten ancestors or by those who lived here eons before your people came to this land. What can we do with this folk belief in a gaming context?
Maybe your party shows up in an isolated village to find the locals practicing this peculiar superstition. The villagers insist that folks who sleep unprotected by a stone-age tool tend to disappear in the night. The locals don’t know it, but the truth is that the ghost of a saber-toothed tiger has haunted these woods for tens of thousands of years. Like Kipling’s great tiger Shere Khan, it both hates and fears humans. It will kill anyone it comes across at night, but avoids stone blades. The beast was struck down by them in life, and can now smell them, even buried beneath a house. PCs sleeping in a tent or wandering the woods at night are likely to encounter this supernatural predator.
This adventure hook works on its own, but you can also fold it in as local color in any isolated, inhabited setting the party visits for some other reason.
A saber-toothed tiger that fears what it recognizes as a weapon raises a neat idea: what if ghosts at your table only fear weapons that they would have recognized in life? Heck, what if they can only be hurt by weapons they would have recognized? Your laser gun and vibro-sword are no use against ghosts who died before the weapons were invented. It turns an otherwise stale combat (“Ghosts? Again?”) into a neat puzzle.
You’ll have to do some fine-tuning of the puzzle to suit your and your players’ tastes. Will the ghost of a 16th-century highwayman recognize a modern fireman’s axe? The sensible answer is yes, but if your players enjoy involved puzzles, the ghost may be supernaturally literal. The PCs may have to break into a museum to steal a wheellock pistol. If you shoot him in the back with it so he’s not aware of what happened, does it hurt him? When he turns around and sees the smoking gun in your hand, does a wound suddenly appear on his body?