By making use of the clues found in the "Postboxes" series, complete the following:
S (Z+Z-S)(E7).(82E) E(Z-A)(E+T+E+C).(493)
This will give you the final location for the cache. This cache has space for trade, please keep the items of decent quality. Please ensure that the box is properly locked after you have found it. If you encounter a problem, press the buzzer at house #5 - if the CO is home, he may help you out.
What do the letters of the Postboxes series spell out? Just my thoughts on the world at large.
Note: The cache has a little frog Geocoin, for the person who is FTF to keep.