The Bay Of Islands would have to be the 'jewel of the north'. Paihia and Russell are the the main centres. These two spots  would be the ideal base for your B.O.I. stay. Activities can be water, land or air based.
Rawhiti is about 29 km from Russell and offers beaches, walks and accommodation. The walk between Oke Bay and The Cape Brett Lighthouse offers some splendid views.
The land is mostly owned by The Department Of Conservation (D.O.C.) The track is approx 20 km long with some steep parts getting up to the main ridge. You have to have a reasonable to good level of fitness to attempt this track. Payment must also be made in full before starting to ensure getting the combination for the door lock of the hut. Bookings be made at

Russell Visitor Centre
PO Box 134 The Strand
Russell
Ph: (09) 403 9005
Fax: (09) 403 9009

 

D.O.C. has a web page  that they change the address to every month or so. The home address listed seems constant so you will have to navigate from there. Sorry. That tells a lot more about this track and others under their control. A good eight hours daylight should be allowed for the inward journey and you have to be completely self sufficient. There is no cooking equipment, bedding or food at the hut.
Water should be carried for the trip in as well due to no reliable sources in the summer. If you wish, this company offers guided tours.
Another walk near Rawhiti is to  Whangamumu. This is an easier track which  you wander through scrub and grass this takes just over an hour. The walk starts about 1 kilometre along the Rawhiti road on the right. At walks end the remnants of an old whaling Station will become evident. It was operating from  the early 1890s and continued till 1931. A little of the history can be found here. Not much remains apart from the building sites and some concrete tanks. This track also extends to the Cape Brett walk if you wish to do the full length.

Places to stay in the Bay Of Islands