Well, I'm thinking of an idea of an event where:  In one particular town or city, someone (probably a kid) has lost something in the ocean, in a forest, in a cave, in an abandoned house, in a fountain.  Basically something is lost somewhere and the kid wants it back badly, and whoever finds it for this kid gets a valuable reward.  But who knows what waits along the journey towards this lost object and who knows if somebody already has it and wants to keep it?