Many years ago, a visit to the Piha Blowhole was part of the Piha experience. I remember standing on the top edge of the tunnel, watching the surf blast through into a grotto, but it seems to have been largely forgotten. Perhaps it’s because it’s not much of a real blowhole anymore. There is also much more scrub and pohutukawa growth obscuring its location, including the cliff edge vantage points.
But there is a short walk down to the grotto. Depending on the conditions and the tide, you may be able to wade/walk/swim through to a beach on the other side of the tunnel. An Auckland City sign provides appropriate warnings and an accessible life buoy if you run into trouble!
To find it, continue round from The Gap, or the end of the Tasman Lookout Track, then push into the scrub more or less where the track ends. If it takes more than a few minutes to find the grotto and tunnel access, you’re in the wrong place. Once you’ve found it, you should also be able to see the rather indistinct track that takes you to the cliffs above the tunnel.