Turning to the force field device, I inserted the blade of my sword into the beam emanating from both sides of the green-colored box.
-Warlord of Ghandor
The Earthling hero of Warlord of Ghandor (who, by the way, never seems to lead any armies; he seems to be about as much of a war leader as is the 4e Warlord class), who has found himself on an iron-poor planet, comes upon a force field generator. It can only be deactivated by putting a piece of that ultra-rare metal, “iron”, on both sides of it. The hero has one of the iron keys; lacking the other one, he uses his steel sword he brought from Earth!
Turning this into a D&D puzzle: a macguffin can only be activated (or deactivated) by placing objects of some rare metal in two places. Whatever the metal is, the players should have exactly one item of that type, preferably in use as a PC’s main weapon; for instance, if someone has a Cold Iron sword, then cold iron is required. (The item isn’t used up, by the way.)
The players need to find a second piece of cold iron – which may lead to some player-directed questing, giving the DM the opportunity to dangle a few adventure hooks with other pieces of cold iron as bait.
Or, if the PC’s think of it; if they don’t mind giving up a valuable resource; and if there is some urgency to the macguffin-activation, the cold-iron-armed PC can snap his sword in half and use the two pieces to complete the ritual.
I like this incident, culled from what is, on the whole, a fairly ordinary sword-and-planet novel. It’s a mini-puzzle, adventure hook generator, and resource management decision all rolled into one.
I’ve come up with four blog posts from this one book, so you might get the idea that Warlord of Ghandor is worth reading. Let me dispel that idea by quoting the following paragraph:
Mauve in color, the creature was a frightening sight!