Gasping for breath, I dragged myself the last few metres up the track and onto the plateau. There had to be some energy chocolate left in my pack - I'd earned it.  I was halfway through the Tongariro Crossing and it would all be downhill from here.

I'd set out early that morning with a group of friends to make the 18.5km journey over the mountain. The air was crisply cold and I was glad of my hat, gloves and ever-so-attractive long johns under my shorts.

The start of the trek through the Mangatepopo Valley was picturesque, as we walked through a rocky landscape of alpine plants, frost-covered grasses and icy streams.

Tongariro and its neighbour Ngauruhoe towered over us and we all made frequent stops to take pictures.

Soon the track started curving upwards. I was moving at a decent speed, admiring how sturdy I felt in my hiking boots and feeling suitably outdoorsy.

We'd been walking for an hour or so when disaster struck, in the form of the steep climb from Soda Springs to the South Crater. I'd thought of myself as fairly fit, so I was pretty surprised to find myself in a crumpled heap at the side of the track, huffing and puffing as others trotted nimbly past. I started to wonder if someone had hidden weights in my boots. It took me frequent rests and a snail-like pace to get to the top of that section of the tramp.

Next we crossed the South Crater, a vast, flat expanse of frozen red mud with rocky cliffs all around. We could have been on another planet - until I reached the other side, turned to check out the glorious view and saw that for an alien landscape, it was looking extremely well colonised. A continuous stream of trampers snaked across the landscape below. Guess we weren't the only ones who were taking advantage of the public holiday.

And there I was at the halfway point - if I chose. From this point trampers can tack an extra hour and a half onto their journey and head to Tongariro's summit. (The really keen - and experienced - can also add the practically vertical climb up Mt Ngauruhoe).

Down below was a series of vividly-coloured pools - the Emerald Lakes, and a little further on, the Blue Lake.

Despite the sunny day, the wind was whipping around my face and making my chin numb as we started the descent.

I bent down to touch the ground and found it radiating heat - the crater is active and there were hot spots and patches of steam dotting the landscape.

The track to the lakes is steep and covered in loose rocks. We slid and skidded our way down with varying degrees of grace, and found ourselves a lakeside spot to collapse and eat our lunch.

We'd been lucky with the weather so far, but as we struggled back to our feet the cloud was closing in.

For the next couple of hours we moved steadily down through the misty mountain passes as the path snaked back and forth to the Ketetahi Hut, the last stop before the end of the track.

The last section of the tramp was pure slog. My legs were aching from the relentless downhill motion, but I was trapped in the rhythm, my eyes fixed on my friend's boots in front of me. If I stopped now, I'd never get going again.

As we moved down off the mountain, native bush rose up on either side of the path and engulfed us... and then we were out, blinking as we emerged into the afternoon light in a gravel carpark.

It was over. I'd finished the Tongariro Crossing. And as I sank into the seat of the shuttle bus that would take us back to the start, I promised myself I'd never go uphill - or down - again.

Well, maybe in a little bit. In fact, that Ngauruhoe climb looked kind of fun...

Find out more about Tongariro National Park.

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