At the cache location, there were used to be a railway passing 3 old ancient tunnels. Now, a bikeway replacing the railway going through them. It is quite safe to walk or bike in these 3 tunnels.
Stage 1:
The cache is a multiple leading you come from one side to another. Please find the Stage 1, how many butterflies in 15 meters? The number is A.
Final:
The calculation of coords for final cache is simple too...
N24 35.(955 + A*10) E120 43.(536 - A*10)
The cache is hidden very easily. Please don't dig anything.