I'm slightly biased as I live next to it, but this is one of my fav beaches in Sydney! It has scenic views out of the harbour and is quietly nestled between North Head and Little Manly. It's always quiet and makes an idyllic spot for a romantic picnic or a chilled day on the beach (it's national park, so you can take booze!). There's a jump rock there too if you dare. You can swim in the calm waters and feel a world away from the hustle and bustle of the city.
It sits just below the North Head which is provides a wonderful, quiet walk and some spectacular views (especially at sunset) of the city.
New South Wales 2093, Australia