This cache is a Wherigo based on Waldmeister's reverse Wherigo cartridge.
The cartridge can be downloaded here.
You now have a "reverse cache box" that displays the distance to the final geocache, not coordinates.
The goal is to ask for the distance as infrequently as possible and find the geocache using only this distance information.
To play, you will need three 6-digit numbers.
To obtain these, first go to the listed coordinates. There you will find a black stone tablet. On it, you will find two 4-digit numbers.
Let these be:
abcd-efgh
Calculate the starting code for the cartridge as follows:
a (a-e) c e c f
(a+e) (e-h) (a+h) h (a-h) c
(c+h) a b d (c-g) g
Have fun!