Nor am I exceedingly fit; regular pilates and walking the dogs hadn't quite prepared me for the aerobic demands of mountain climbing, but more on that later.
Tongariro National Park is a World Heritage site, the crossing, one of the top 10 alpine walks in the world. What makes it top 10? The volcanic landscape, the diversity of the climb, the fact you can do it in one day.
There's no doubt about it, this is a challenging walk and we're about to tackle it in challenging conditions. Stew tells me the winter crossings are his favourite. I can see what he means. The snow and mist give the mountains a mystical, ethereal quality and there are no crowds. We seem to have Tongariro to ourselves.
We enter from the Mangatepopo Valley, following the stream up hill. No snow at this level. It's easy to see why Sir Peter Jackson chose this place to represent the evil kingdom of Mordor in his Lord of the Rings trilogy. It is barren, unforgiving, forsaken even by the birds.
I marvel at Soda Springs, a waterfall that magically appears from the rock, no stream above it, just one of the thermal wonders we'll pass today. It's a relatively easy walk for the first three or four kilometres and then we hit the notorious Devil's Staircase. A 45-minute haul, pretty much straight up. And it literally is a staircase. DoC has put a lot of work in here and the steps certainly make it easier, but even so I'm gasping and needing frequent stops to "admire the view".
Stew assures me I'm fitter than I think and that I'll manage the climb. I wonder if that's what he tells all his clients.
No sooner have we reached the top of the staircase and levelled off than we are climbing again along the ridge that links Ngauruhoe and Tongariro. It's a narrow ledge between the south and red craters, a steep drop down one side. I'm trying not to look.
There's snow here, and the wind has come up. It is suddenly icy cold and the view has gone, replaced by swirling mist and cloud. I'm struggling to stay upright and Stew gets me to grab on to his strapping with one hand while I use my ice axe for support in the other.
Just when I'm beginning to think this wasn't such a great idea, Stew points out the summit. I summon up the last ounces of my strength and we strike out for the top. I can't tell you how exhilarating it is standing at the top of a mountain, we'd climbed to over 1800m.
That, I think, is the really special thing about this walk - the sense of achievement for an ordinary person, one who is not used to great physical challenges, to get to the top, it's miraculous.
We slide in the snow down the steep sides of the central crater on our backsides, whooping and hollering like a couple of kids. We lunch beside the exquisite, steaming Emerald Lake, before heading up through the notch, along the face of the silent north crater and down another DoC masterpiece of stair work, zigzagging to the Ketetahi Hut where we rest at last, taking in the stunning view of the hot springs, steaming away and Lake Rotoaira in the valley below.
We leave the mountain as easily as we arrived, with a stroll down through the bush, on this southern side, alive with the sound of birdsong and the rushing waters of the Ketetahi stream. The crossing had taken us seven and a half hours.
Just hours later, the hut would fall victim to the Te Maari crater's eruption. Huge boulders would be hurled through the windows. We were lucky.
The next morning I was woken from my slumbers at the Hilton in Taupo by a text from Stew: "We timed it to perfection," he said, "Tongariro erupted at 10 to midnight. I'm up the mountain waiting for the sun to come up!"
The last eruption happened more than 100 years ago.
I celebrate my close call and triumph on the mountain with a mirimiri or Maori massage. The Wairakei Terraces thermal spa is a family business. Raewyn and Jim Hill have recreated Tarawera's famed pink and white terraces here and they are truly remarkable.
Thermal water cascades over the natural silica, ending in a series of pools where I soak away the strains of my mountaineering exploits before my massage. The mirimiri takes place in a tiny, old, wooden whare. This massage tends not only to your muscles but also to your mind and spirit.
The masseuse prays quietly over me as she works, ancient karakia handed down over generations. There is a particular karakia, she tells me, for each part of the body.
It works wonders. I am truly unwound. Bliss.
Bigger blast fear keeps track closed
Researchers from GNS Science are still studying the mountain after last week's eruption, so travellers will have to cool their heels before the popular Tongariro crossing track is reopened.
Mike Rosenberg, of GNS Science, was yesterday hoping to put together much of the evidence and get a better idea of what had happened.
"I'm hoping that today there will be some consensus and a clear and consistent message about what's caused the eruption and what's likely to happen in the future."
Department of Conservation staff say they are working to reopen the tracks and huts on Mt Tongariro as soon as conditions are safe. But it is not known when trampers will be allowed on the Tongariro Crossing.
For the latest updates, see doc.govt.nz or gns.cri.nz.
CHECKLIST
Tongariro Crossing: Adrift Guided Outdoor Adventures offers a winter guided Tongariro alpine crossing for $155 a person.
The Mind, Body and Soul package includes a night's accommodation at Hilton Lake Taupo and a half-hour spa treatment and soak at Wairakei Terraces from $350 a night.
Further details: See greatlaketaupo.com/grabit or call 0800 Lake Taupo or 0800 Turangi.
* For more on the region, see our Tongariro National Park travel section.
