Martins Bay is on the southern edge of Scandrett Regional Park on the Mahurangi Peninsula. It is a beautiful white sand, safe swimming beach that faces east into the Hauraki Gulf. The view from the beach looks out at Kawau Island, Motuketekete Island, Moturekareka Island and Motuora Island. It is less known than other beaches on the Matakana Coast of Auckland, and a bit further to get to, so it's not quite as busy. There is also a substantial campground behind the beach with various accommodation options.
A stroll along the south end of he beach is especially attractive with some amazing pōhutukawa trees hanging off the edge of the grassy reserve behind the beach. Go pick out a picnic spot under one of the trees. There is also a pontoon you can swim to and jump into the water.
At the north end of the beach, there is a sign for Martins Bay Track. Thai takes you to Scadrett Regional Park, which provides further opportunities for exploration.
Martins Bay is a one-hour, 77 km drive from Auckland Downtown. Take the northern motorway to Warkworth, then Sandspit Road, Mahurangi East Road and Martins Bay Road to the car parks towards the bay's south end.