This is a "reverse" Wherigo. The geocache is NOT at the posted coordinates, and you do not even need to go there to start.
The idea is that you can start from anywhere, click on the "box" to get your distance to the geocache, then reposition yourself and try again to see if you are closer or not. By successive guesses you find your way to the geocache.
The cartridge is available to download from the wherigo.com website and was created by Waldmeister.
Enter these 3 codes:
104365
830750
763585
Good luck and have fun!