The next stage of the journey is a bit of an adventure in itself: at Little Huia the sealed road runs out and we have to drive through a ford, before starting to wind up over the hill and into the Whatipu Valley.
We are keen to explore the sea caves in the hope of finding leftover pirate treasure, or at the very least large crabs, but are thwarted in our efforts to find the track, which has decided it is actually a stream. (The Auckland Council website understates: "Some sections become waterlogged after wet weather." Quite.)
We decide to leave the caves for another day.
We trudge through the sandhills towards the beach. Whatipu is vast, stretching north along the base of the cliffs and wetlands to Karekare. At the track end of the beach there is a large expanse of black sand, separated from the outer beach by a shallow lagoon, and to the east the sand-locked Paratutae Island, guarding the entrance to the Manukau Harbour.
We walk this way, joining other groups of walkers, families and some young guys flying a drone in the clear, calm air. The day is so clear we can see as far as Mt Karioi at Raglan, which looks like an island rising out of the reflective surface of the sea.
A huge log - a whole tree, really, blanched white by sea and sun - makes a great balance beam and the shallow lagoon is good for paddling in. There is plenty of space to run around and the bumpy volcanic lower slopes of Paratutae are interesting for the kids to explore. The sands have reclaimed the kauri timber tramline that used to run along the shoreline and the remains of the wharf at Paratutae are no longer visible but there are traces here and there, old timbers and rusty fastenings.
As we head back to the car, the black sand has become hot beneath our feet. We had grand plans of visiting the Huia Settlers Museum to find out more about the 1863 wreck of the Orpheus on the way back, but the combination of sun, sand and fresh air means both kids are fast asleep before we have driven more than a few kilometres.
The west coast is a far cry from the golden sand and sheltered waters of the East Coast Bays. It's a magical place to visit, and we will have to come back and explore those caves.