The cache is not at the listed coordinates, however those are a good place to start the associated Broken Bay Sands Adventure Lab, which you must complete to obtain this cache's coordinates.
The Adventure explores the shoreline sands at Ettalong Beach, Half Tide Rocks, Ocean Beach, Umina Beach and finally at the Umina Point headland where this bonus cache is hidden nearby. On foot along the beaches it's about 3.7km, but you could also cycle the disjointed shared bike paths or drive to each location. There's a frequent bus service between the Umina Beach and Ettalong Beach shopping centres if you don't want to walk both ways.
The cache container is a one litre Sistema sandwich box concealed behind some sandstone camo. A pencil is included. Please make sure to rehide it completely out of sight as this spot is frequented by inquisitive muggles.
Access to GZ is best done at low tide. The recent rains have also led to a build-up of slime on the rocks so take care with your footing. Approach the cache from the rock shelf at sea level; there's no need to climb the cliff or into any vegetation.
Congratulations to Mr&MrsFish, the first to traverse the sands!