This Wherigo will gives you the distance to the cache's final location based on your current location. You have to find the cache using only this info. Try to find the box with as few queries as possible and share your number of tries in your log.
The cartridge can be downloaded from here. You can start wherever you want but the final location is close to the city center of Sofia, Bulgaria.
In case the cache is missing I will appreciate if you place a temporary container until I do maintenance. Happy geocaching!