The starting location shows a pair of anchors outside the Yacht Club (you don't need to go there), they are not the only large anchors along the foreshore in Williamstown.
There are so many. The Adventure Lab shows you five.
This is the Bonus cache associated with the Adventure Lab: Anchored in Williamstown.
To find an Adventure Lab Cache
Download the free Adventure Lab app.
Log in with your Geocaching.com account.
Select Anchored in Williamstown from the map or list.
Navigate to the Adventure location and follow the instructions in the description.
To find this cache you need to assemble all your answers from the Adventure Lab in order, A to P.
Then use the formula: South 37 5P.FCL East 144 5G.JN(E-D-K)