Whites Beach, to the north of Piha, and Anawhata to the north of Whites, are the two true gems on the west coast. Neither have direct road access, so you must walk in on relatively steep paths.
Whites is accessible from North Piha by crossing over Te Waha Point. The track entrance is a bit obscure, but there is a sign on the forest's edge at the beach's north end. It is a reasonably steep climb up to the Point, with amazing views back to Piha and of Whites. Try and be there as the sun goes down!
There is an easy track down to Whites from Te Waha, or you can take the less obvious “goat” track across the face of the point until you find a guide chain. Then, follow the chain down to the edge of the beach. It is much quicker, more exciting, and only a bit scary. Note that it may not be doable at high tide.
You can also access Whites from Piha via the longer White Track.
You probably shouldn’t swim at Whites as it’s unpatrolled, but people do.