State Highway 12 is an interesting and very scenic drive - allow time for stops, there are plenty of good eating places at Opononi with great views over the harbour. On the way the Railway Cafe at Kawakawa is also "highly recommended".
There is a very good article on the Hokianga Harbour here Wikipedia
Scenic lookout at the mouth of Hokianga Harbour
near Omapere - an easy 20minute walk from the carpark
near Omapere - an easy 20minute walk from the carpark
Looking south from the route to the lookout
Inner harbour beach and amazing clear blue water
Harbour entrance
Inner Harbour looking towards entrance
Tane Mahuta
Wikipedia
Wikipedia
Near impossible to do justice to this huge tree in a photo. Estimated to be between 1250 and 2500 years old and it has a circumference of almost 16m or a diameter approaching 5m. (2002 measurements )