I once went to Pmx's scavenger hunt, which was pretty fun as you had to go through the clues until you reached the end for a prize. I think a large scale version as an event would be pretty cool. However, when I was doing the hunt in the town I got inspiration from, I realized people were just walking by, and you could probably find the ending by following them, making the hunt pointless. So as a solution, you could make everyone invisible--like the parkour option allows (but without an option)--, and go from there. It would have to be done with a new map every time it is hosted, so perhaps make a few maps before hosting the first one. There could also be hunts based on holidays such as Christmas, Valentines Day, Saint Patrick's, etc.
Not sure about the prize, but it would most likely be meebles.
