Sealink ferries sail from Wynyard Wharf in Auckland to Tryphena on Great Barrier Island. The four-hour-long trip costs $84 one-way or $105–152 return (the more expensive fares are during peak periods such as summer and public holiday weekends).
Tryphena Wharf is the most conveniently-located spot to arrive on the island, but it is still around a one-hour walk from the general store, pub and most accommodation in Tryphena.