Without a doubt is has been the KCoploy caches created by Steve and Mary Brown in the Kansas City Metro area.
http://www.geocaching.com/seek/cache_detai...64-a49b24c6ae2b
You seek 24 different micro caches in the entire metro area to collect the passwords and "clues" around the cache which relate to the standard Monopoly Board. Once you have all 24, you get the coordinates to the Grand Cache. Very fun way to explore a city from east to west, north to south, on both sides of the state line. Also very instructive way to introduce children to the entire city and to the living conditions of people all over the metro area.
A blast!