This is a bonus physical cache for the Adventure Lab Built Heritage - Old Noarlunga. You must successfully complete the Adventure Lab in order to find this one.
Play the Adventure Lab: https://labs.geocaching.com/goto/OldNoarlunga
The Adventire Lab has 5 locations each of which will give you a clue to the final location of this cache.
The cache can be found at: S35° 10.ABC E138° 29.DE(D-B)