The cache is NOT at the listed coordinates. If you try to go there you'll drown and be eaten by sea monsters.
The 5 Lands Walk is a 10km coastal trail linking the communities of MacMasters Beach, Copacabana, Avoca Beach, North Avoca and Terrigal. Each year in June is a community walk along the route with arts and crafts displays, entertainment, food and free shuttle buses, but the trail can be walked at any time of the year and is well signposted.
The associated Adventure Lab is 5 Lands Walk with its starting place at MacMasters Beach, although its locations can be done in any order. Each location has easy road access for those not wanting to do the walk.
This bonus cache is hidden close to the route between locations 4 and 5, so for the benefit of those doing the complete walk from MacMasters, the coordinates are fully revealed from the first four locations, with numerical values given for the letters A, B, C and D in the Adventure Lab's completion journals. The cache is located at:
S 33º 27.DAC
E 151º 26.CDB
Access is along a short cleared track from the road which should be obvious when you draw level with the cache. The container is a "mega" Bison tube (90mm length by 55mm diameter) with camouflage colouring. You'll need to squeeze into the undergrowth to reach it. There's a cliff near GZ but the cache is well back from the edge. A pencil is included but bring a pen just in case.
Congratulations to Mr&MrsFish, the first to complete the Adventure and bonus!