The Tawharanui Regional Park (Info) is 82km north of the Auckland CBD (on the east coast) and although I have fond memories of the place from when I used to camp there back in the mid 1990s I haven't been back since as it is twice as far away as my favourite (but much smaller) park - (Wenderholm)
The road to the park is sealed except for the last 4km which is currently being completely reconstructed - if it is wet expect to get your vehicle very dirty.
It's a large park - several km from end to end with many really spectacular beaches, sections of gnarly coast and a very picturesque lagoon near the entrance.
On the day we were there (a Friday in September) there were only about eight other park visitors including some very poor souls on a modelling bikini shoot in the freezing cold.
View from the ridge about half way along the park - looking west
Lagoon near the entrance to the park
Many sandy beaches
...and some stony beaches
Typical view below from one of the many walks
The birthday girl on her day out - before the shoes got really muddy on one of those walks.
(Photos Canon G16)