Stuff's travel journalist Brook Sabin explores a hidden treasure between Rotorua and Taupo that is sure to be a great adventure.

We've just arrived at a geothermal treasure. Steam and sunlight flirt in front of us. And in the background, a hot waterfall - the temperature of a bath - thunders away. It's a scene of such beauty and mystique that it almost feels fictitious.

Aside from a handful of locals - few people know this place exists. It's protected by nature's best defence: isolation. We're half an hour drive out of Rotorua, and an hour down a river by jet boat. Then it's 20 minutes of wading in a hot water stream down a narrow crevice. Sound a bit daunting? Well, consider this: the youngest person to do it was just three.

Orakei Korako is a little-known valley of geothermal wonder - sitting between Taupo and Rotorua. It has 23 geysers, tucked away in the hillside. The surrounding bush is a constant hiss of steam, unpredictably mushrooming as Earth vents its anger. While anybody can visit the geothermal park, getting to the waterfall is much harder. Part of the geothermal park drains into a series of rocks, which has formed a narrow gap you can squeeze through.

The only way to get to the entrance is by jet boating down the Waikato River - passing at speed under trees, around rocks and through a remote gorge. It's the middle of winter, so the crew wrap us up in seven layers for the hour-long boat ride.

As we near the geothermal valley, the bush begins to change dramatically. Steam rises in dozens of places, from hidden fumaroles on the forest floor. We head a few more minutes down the river, to a small steam. To our surprise, as we jump out of the boat, the water is already warm - a sign of what's to come.

Now, here's where the trip gets its name. It's called 'The Squeeze'. The stream quickly becomes a narrow crack in the rock, just wide enough to squeeze through. Depending on the time of year, the water can be around your waist - or in places - you may not be able to touch the bottom.

It's not so tight you need vaseline to get through, but it will test your relationship with small spaces. Our guide, Cam, has only ever had about ten people freak out and refuse to keep going.

It's five minutes of shimmying before the crevice opens up again to thick native bush. By this time, the stream has got even warmer, leading to a thick layer of mist hanging in the air. The beauty is mesmerising.

Before long we hear a roar of water. There's one last squeeze to the waterfall pool, complete with a canopy of thick ferns. There is no cellphone reception, no sign of the modern world - I'm literally up a crack in a volcanic valley - sitting in a natural hot bath. Now that's my kind of hidden gem.

MORE INFORMATION NZ Riverjet runs The Squeeze trip year-round. $189 for adults and $99 for children. See: riverjet.co.nz

GETTING THERE Riverjet is located between Taupō and Rotorua on SH5.

-Stuff.co.nz/Brook_Sabin