And put a timed execution device (a swinging blade? Guillotine?) over the prisoner. If someone doesn't rush in within 3 rounds and disable it, then the prisoner dies.
That's a great idea, but ... mage hand. (Sigh)
Again, mage hand. And there was actually quite a bit of treasure in the last dungeon that the PCs voluntarily passed up just because they were afraid it might be trapped or cursed.Add lots of treasure to the dungeon. Brilliant gemstones hidden under overturned mugs. Caches of gold hidden behind hanging portraits. That's how you reward players for interacting.