Update June 2025 - calculation changed, cache in same location.
Welcome to another in the GSM series. You are looking for a custom container in a wonderful park. I hope you do not encounter guests at GZ which will restrict you from completing the find.
To find the cache, you will need to gather some numbers to find GZ which is a short 200m walk to:
S 34 49.BB5
E 138 5B.1AB
where
A = number of tennis courts
B = A-1
Minutes checksum = 40