The Shakespear Regional Park was resently reopened after the erection of a preditor-proof fence at Army Bay. The open sanctuary shares the end of the Whangaparaoa Peninsula with the New Zealand Defence Force, making the park seem remote, despite over 50,000 people living within 30km of the park.
The Tiritiri Track is one of the less popular tracks, but offers some of the most spectacular views to the East of the Peninsula. The track follows the Shakespear Bay beach, through the campground and into the hills.
I'm not certain of the purpose of the concrete bunker, but it appears to still be in use.
The cache is about a 15 minute walk from the campsite, or a 25 minute walk from the public carpark. Highly recommended a longer hike from the Park entrance, via "Lookout and Smile" (GC39GFZ) - well worth it :)
The cache is North of the bunker. It is a plastic 500ml take-away container. The cache contains a logbook, and a pencil.