The Tongariro Crossing, central North Island, is described as "the best one-day walk in New Zealand". This tag appears on countless brochures and accounts.
It is right and it is wrong.
Right because the Crossing combines petrified lava flows, mountain peaks, volcanic craters, thermal activity, herbfields and bush - all in one fantastic day.
It is also wrong. This is a mountain track. To call it a walk tends to belittle the potential dangers of any mountain track. You need trekking boots; warm jacket, thermal leggings, woollen hat/gloves, drinks and food.
Of course, you might strike fine weather throughout and those warm clothes remain in the backpack but at least you'll know you can deal with anything the mountain elements throw at you. You'll enjoy a day that will be one of your best travel memories ever.
Go unprepared for sudden changes of weather or temperature and you could face difficulties - there have been occasional deaths on this track.
We start off at 9am from the carpark at the end of Mangatepopo Road (6km off State Highway 47). Gentle at first - there are waterfalls, banks sprinkled with wildflowers and herbs. The track winds beside, and sometimes across, the tumbling Mangatepopo Stream.
We walk past petrified lava flows from Mt Ngauruhoe, very much an active volcano. Some of the tortured lava blocks make weird 'sculptures'.
Soon we're labouring up the Mangatepopo Saddle, which is a jumble of lava rocks. There's no real track, just a tortuous twisting way up, marked by poles.
My fitter-than-me companion makes encouraging noises as I labour up, doing a fair amount of gasping and panting, always looking up towards the summit. It's 1660m but I finally get there. A battering blast of wind forces us into those extra jerseys, jackets, gloves and woolly hats before crossing South Crater.
This is flat like a speedway track, with a scatter of rocks that have been flung out by various volcanic explosions. The flatness is bliss after the climb up the Mangatepopo Saddle, but shortlived.
Soon we're zig-zagging upwards again, on loose scree and rocks, cheered at times by mountain buttercups gleaming gold in rocky crevices. Strong sulphur smells announce the Red Crater. This is the highest point of the track at 1820m.
It is a surreal world. There are fumeroles with dragon-breaths billowing out of them; rock-walls that leak more thermal steam and a large, evil cleft in the mountainside. A setting for Dante's Inferno!
Every now and then steam blows across the track and blocks our vision. We view the crater at a crouch. Standing near the edge feels distinctly perilous in this wind.
We start downwards, slipping and sliding on the cinders, drawn towards the magnet of the twin Emerald Lakes. These are old craters that have filled with water. Their 
brilliant emerald colour is due to minerals that have leached from the adjoining thermal area.
We choose a sunny spot for lunch beside one of the lakes. But the wind brings a chill with it. So we're off across Central Crater and past Blue Lake, another old vent.The saddle at the northern side of Central Crater presents no problems to graduates of the Mangatepopo.
Here the world is at our feet. Stretches of mountainside clothed with foliage, a ring of bush at its base; Lake Rotoaira in the near distance; Mt Pihanga and Lake Taupo further off.
We set off downhill on a long, long trail a-winding. The track zig-zags back and forth along the flanks of North Crater. Tongariro was once cone-shaped, like nearby Ngauruhoe, but a mighty eruption blew the top off, leaving several distinct craters. Both its neighbours are active volcanoes.
Slopes are cloaked with Alpine plants, carpets of herbs and cushion-plants. At Ketetahi Hut we make use of flushing loos (always a relief on a wilderness walk where basic long-drops are more usual).
Ketetahi thermal area, near the hut, has steaming fumaroles, blowholes and boiling mud.
The track falls steeply, with long stretches of steps. Tussock gives way to herbfields, but the steps seem to go on forever and it's not long before my knees start objecting strongly.
But soon we're into a flatter area of ferns, tall totara trees and mossy banks. Okahukura Bush is a cool, green, restful place after the wind-blasted heights.
The meandering track gives you time to reflect on the astonishing variety of sights that a single day's walk has presented. Best one-day trek in New Zealand? Sure is!
Information credit: Judith Doyle: read more adventures as Judith takes on the Whanganui River
