The Bay of Islands, in far northern New Zealand, is most easily accessible from Auckland. Here are the options for getting there.
By Rental Car or Private Transfer
Many travelers to New Zealand like to rent a car, which gives them flexibility to stop at out-of-the-way spots. While Kerikeri is the largest town in the Bay of Islands area, most travelers head to Paihia, which is a good base for exploring must-see places like Russell and Waitangi.
Paihia is 140 miles (227 kilometers) north of Auckland, or three hours' drive along State Highway 1. The roads are good, but mostly two-lane highway rather than multi-lane freeway, and winding in places. To break the journey, Waipu and Whangarei are good towns for a comfort stop or meal.
There are daily flights between Auckland and the Bay of Islands Airport, just outside Kerikeri. They take less than an hour and can be quite scenic when the weather is good, as they follow the coastline of eastern Northland. If coming from other parts of New Zealand, you'll need to transit in Auckland.
A daily bus travels between central Auckland and Kerikeri (and beyond). You can get off at Paihia if you prefer. The journey is a bit slower than traveling directly by car, and takes between 4 and 5 hours. The buses are large and comfortable, and make comfort stops at designated places.