To find this bonus cache you will first need to complete the Nelson Creek Recreation Reserve Adventure Lab.
After successfully completing each waypoint of that you will be given some information towards assembling the final coordinates for this cache.
You will need to bring your own pen and you will find it at S 42° 24.ABC E 171° 31.DBE
To begin the Adventure Lab cache you need to download the app to your phone from the following link:-
Android: link
Apple: link
This QR code will then get you started
You will need to bring your own pen and there is no room for trackables.