This cache is at the tip of Bradleys Head and has a gorgeous view across Sydney Harbour. It can be accessed via a short walk along the beach and across the rocks, but be prepared to get wet feet if the tide is high.
Whilst it's not far from the car park near the amphitheatre, I would recommend parking just inside the National Park gates (the car park is on the left just after the turnoff from Athol Wharf Road). From there you can take the Bradleys Head and Chowder Head walk to enjoy the scenery, and check out the remains of the convict-built battery and the mast of the HMAS Sydney (I) when you get there. You can head back via the Angophora Walk and take a dip at the beautiful little beach on the way. The round trip is approx. 2km.
** Please note: the parking inside the National Park is metered, however you may be lucky enough to find a free spot down by Taronga Zoo Wharf if you don't mind walking a little further.