Opoutere Beach, New Zealand
This beach is just off State Highway 25 between the Bay of Plenty and Coramandel. It's about a 2 hour drive south of Auckland.
There is a car park with toilet facilities. From there a path leads through a pine wood onto the beach, about 10 minutes walk. The area to the right, including the beach, is a reserve for an endangered small wading bird, the New Zealand Dotterel. This confused me a bit as I have only ever seen our UK dotterels high up on mountains.
Opoutere is a beautiful wide beach, sheltered by the trees, with shapely islands offshore. The sand slopes gently into the sea, (actually, the Pacific I suppose), and as far out into the water as we went, the bottom was entirely sand.
Can't go without recommending the superb naturist campsite at Kati Kati, about an hour to the south, too.
Alas it's so far away I'm unlikely ever to get back there, but if you have the chance, go New Zealand and enjoy the wonderful, empty sub-tropical beaches of the North Island.