The type of cache I linked to is a Locationless (Reverse) Cache.
"Locationless caches could be considered the opposite of a traditional cache. Instead of finding a hidden container, you are given a task to locate a specific object and log its coordinates. A scavenger hunt of sorts, it involves collecting waypoints of various objects around the world. Due to the nature of locationless caches they do not come up on the nearest cache page. You can find them at their own location. "
Check out the different types of caches here
http://www.geocaching.com/about/cache_types.aspx
There are even webcam caches---is this cool or what!!