If you are starting from Downtown Auckland, the Devonport Ferry is the best way to get to Devonport on the North Shore. It is operated by Auckland Transport and runs every 20 minutes during peak times and half hourly off-peak. It only takes about 20 minutes, compared to driving, which could take half an hour or more (the traffic can be as bad as it gets in Auckland). There is also the alternate option of the Bayswater Ferry.
The ferry offers nice city and waterfront views, especially at night. To the west of the Devonport ferry terminal, you also travel past the NZ Navy facility, so you will probably see one or two (modest) naval ships. Once in Devonport, you can hike up Takarunga Mt Victoria or start along the North Shore Coastal Walk.
You can use an Auckland Transport Hop or credit card for the ferry.
