There are some things you never think you'll encounter while travelling, such as the fire and brimstone offered as torment to the ungodly in the Old Testament's more excitable verses. The sort of thing you see in church frescoes, where sinners are being thrust into bubbling cauldrons by horned devils with pitchforks.
No one is being tossed into the brew at Wai-O-Tapu, but there's plenty of fire and brimstone, which is an archaic word for sulphur. One of the pools is called the Devil's Bath and is filled with lime-green mud that would peel your skin off. It owes its cartoonish colour to sulphur and ferrous salts that rise up through the earth's bowels, bringing with them the stench of hell itself. Or so you might imagine, because this bizarre landscape leaves you with few other references.
You'll find the Devil's Ink Pots nearby. They aren't as immediately eye-catching, but the round, grey craters burp with boiling mud and steam. They're so mesmerising you start to lean in towards them – surely the devil's work – until the heat and smell remind you to take a step back.
The fencing is flimsy in Wai-O-Tapu. At the Devil's Ink Pots only a wooden picket fence holds visitors back from the salt-encrusted edges of the craters. At one point a completely unfenced boardwalk runs right across one of Wai-O-Tapu's biggest thermal pools. It's a wonder more selfie-enthusiasts haven't fallen in and been instantly dissolved.
From a distance, you get terrific photos of people on the boardwalk, appearing to stride across the surface of yellow and white pools like astronauts from a science-fiction movie. It's the crumpled green hills behind that look curiously out of place, reminding you that New Zealand's placid domesticity is just a thin veneer on a landscape still in creation.
Wai-O-Tapu Thermal Wonderland is 30 kilometres southeast of Rotorua and has a few hokey entertainments, chief among them Lady Knox Geyser, which blows its top daily at 10.15am thanks to human intervention. But the rest is the real deal, and an astonishingly close-up look at nature in the raw, roiling and steaming and with a stink that's half open sewer, half rotten eggs.
This is New Zealand's biggest geothermal area, extending over 18 square kilometres, though the parts accessible to visitors are more compact. Although the landscape isn't grand in scale, it's unlike anything you've likely seen before. The best view over it is at Artist's Palette lookout, across a mud lake and pools variously coloured rust-red, orange or cockatoo yellow.
A highlight is the ridiculously misnamed Champagne Pool, which is neither genteel nor champagne-coloured, though it does have a slight fizz. Its mineral-rich waters are a vivid aquamarine rimmed with startlingly bright orange edges caused by elements such as arsenic and antimony that you'd normally only encounter on a periodic table.
Walkways meander through the geothermal park, which is pockmarked with fumaroles and small craters that leave you wondering whether another might open to swallow you up at any moment. You could hurry around the chief sights in an hour, but paths extend beyond the boardwalks to outlying thermal pools, and are worth a wander.
These aren't sights you see every day, so you might as well take your time. The rocks hiss, the mud blooms in exotic hues. Pillars of salt grow like mushrooms. At one point a big crack in the earth opens up, allowing you to see brimstone streaking the rocks with yellow. Hell on Earth, but really rather thrilling.
Brian Johnston travelled as a guest of Tourism New Zealand and Treetops Lodge.
Air New Zealand operates multiple flights between Australia and Auckland, with domestic connections to Rotorua. See airnewzealand.com.au
Treetops Lodge & Estate sits on 2500 acres of private native forest outside Rotorua. It has lodge rooms and villas, an excellent restaurant and experiences such as hunting, fishing, horse riding and wellness. Rooms from $NZ995 ($935) per night. Phone +64 7 333 2066, see treetops.co.nz
Wai-O-Tapu Thermal Wonderland is a 30-minute drive southeast of Rotorua and is open year-round. Adult tickets $NZ32.50 ($30.50), children $NZ11 ($10). See waiotapu.co.nz