You’re sitting in a hot tub. Kind of. Like usual, you’re surrounded by bubbles and 147°F water. You have an amazing view with a golden beach, blue water, and impressive surfers on one side. A rocky hillside and a rugged forest are on the other. But one thing is very different this time. Your hot tub is made of sand.

Welcome to Hot Water Beach on the east coast of the Coromandel Peninsula. At this unusual beach, hot springs flow underground and calcium-rich water filters up through the sand. For two hours on either side of high and low tides, the beach becomes a natural (and free) spa. It’s one of the most-popular destinations on the North Island.

You arrived early this morning, a few hours after the 6:00 a.m. low tide. You felt like a kid again as you began digging a big hole in the sand. It quickly filled with very hot water. You filled a bucket with water from the bay (to keep you cool), stripped down to your bathing suit, slowly lowered yourself into your new tub, and waved at your neighbors about to do the same. Time to relax.

Hot Water Beach sits in V-shaped Mercury Bay. The bay, which is filled with big yachts and marlin fishermen, was named by Captain James Cook when he explored the coast of New Zealand in the 18th century. A café, a little store (where you can rent a shovel, if you forget one), and an art gallery overlook the beach. More white-sand beaches and lots of seafood restaurants are nearby. Though right now, everyone is focused on the hot beach.

But you only have a few hours to enjoy this beach. The tide is already starting to creep toward you. High tide is around 12:20 p.m. Soon, waves will start breaking down the walls and diluting the hot water. Rip currents will make the beach unsafe. While your hot tub will eventually disappear. It’s time to go eat green-lipped mussels and smoked fish for lunch. Then you can decide if you’ll return for another soak in the afternoon.