The Hole in the Rock cruise is the signature activity in Paihia and one of the most popular day trips in New Zealand. Full-day boat tours leave from Paihia Wharf and head north through the Bay of Islands to Cape Brett, where a sea arch — Motukokako, also called Piercy Island — has been cut through a dramatic volcanic headland. On calm days the boat drives straight through the arch.
The route out passes many of the 144 islands, and most tour operators look for dolphins en route — bottlenose and common dolphins are frequently spotted and sometimes swim alongside the boat. Shorter tours are available (not going all the way to Cape Brett), but the full trip gives you the best chance of the dolphin encounter and the arch passage. Tours take about 5–6 hours; book at the wharf or through your accommodation.