The teeth and fingerbones of holy men and more
The Pool of (add the name of the God or Goddess of your choice) is well known as one of the greatest holy places of the world. It is said to be full of piles of gold and jewels, a place where wishes are granted, wounds are healed, prophets have dreams that come true, and suspected criminals are fairly judged. Pilgrims from the other end of the world have been known to travel for more then a year, braving the perils of disease, brigands and bad weather, just to reach it's holy waters.
The PCs accidently start a fire and are caught by the local law enforcement. Since it was accidental, the punishment for the PCs is to fight the fire. Providing they can put it out before it burns down the town, they will not face any further punishment.