The platform on which I stood, 22 metres up a giant 500-year-old rimu tree, swayed alarmingly beneath my feet as a wind gust whirled through the lush New Zealand forest. Below me was the forest floor – far, far away.

Thanks to the solid steel line I was attached to via multiple straps and a harness, I could, however, lean out over the vertiginous drop without concern.

Turning my attention back to my 70-year-old mother, I watched with amusement as she inched her way forward to the edge of the abyss, a 220-metre zip line disappearing into the distance in front of her. On either side of the zip line, the huge rimu trees loomed like forest sentinels.

“Wait until the wind stops,” murmured our guide, Dan. “Otherwise you will be blown into one of the tree trunks. They are rather hard, and it’s a contest you won’t win.”

This comment did nothing for my mother’s peace of mind, but as the winds died down, she was off – a combination of abject fear and exhilaration on her face as she whirred at speed into the distance.

Now it was my turn. I walked to the edge of the tree platform as Dan’s radio crackled to life.

“Line’s clear!” came the word from our other guide, Joe, on the other side of the zip line.

Three wooden steps down from the platform and then I was clear of the tree and launching into space. A high pitched whir from overhead buzzed through my ears as the zip line took the slack and I was hurtling between the forest giants, while below me the tree ferns blended into a feathery green blur.

Twenty-five seconds later and I was landing on the next platform, again well above the forest floor, while the ancient tree shifted in the wind like a ship’s deck in a storm.

Rotorua Canopy Tours is a new company on the Rotorua adrenaline scene, in a place that abounds with bungee jumps, white water tours, zorbs (massive balls that you get into and roll and bounce down steep hills) and the like.

Endemic North Island robins, tomtits and moreporks (a small owl) are all now reclaiming their forest home. It’s a great example of ecotourism in action

Now over a year old, they offer a canopy tour like no other – six zip lines through pristine native forest, as well as narrow swaying bridges and assorted dare-devil tree crossings.

It’s not all high-speed thrills and chills though. The company are putting their money where their mouth is, and assisting the Department of Conservation in protecting this incredible native woodland. By donating part of their proceeds, the company pays for a large number of traps targeting the never-ending onslaught of introduced predators – possums, stoats and rats.

It’s been a huge success. The numbers of invasive pests are way down in this area now, and the native bird life has rebounded. Endemic North Island robins, tomtits and moreporks (a small owl) are all now reclaiming their forest home. It’s a great example of ecotourism in action.

“This is the last one – time to do a little freestyle, as we are close to the hospital if things go wrong,” said Dan with a grin. I opted for going upside-down and was soon proceeding at high speed, while the forest floor whipped along at dizzying speeds below me. The whole thing was over way too soon.

Having experienced New Zealand from way up in the trees, it was now time to see what it was like deep underground. For this, we drove onwards to Waitomo and its famous glow worm caverns.

The area is riddled with cave systems – over 300 explored so far. Within these twisting, winding depths reside glow worms, the larva of a fungus gnat (or a “mosquito on steroids” as my guide, Mica, put it) that lay out dangling pearl-like strands from the cave roof, illuminate the vicinity with their glowing behinds, and lure hapless airborne insects into their webs for dinner.

One way of seeing the caves is to take a sedate tour through a subterranean lake on a large boat. But, fresh from my adrenaline highs in Rotorua, I opted to take the black water tube trip known as The Labyrinth.

Donning a rather moth-eaten wetsuit, 12 of us trooped off in a minibus to the Aranui cave system. Before us, on the forest path, a tiny crack opened up in the fern-encrusted forest floor. Squeezing our way into it, we descended into the depths, each of us bedecked in helmet, head lamp and clutching a rubber ring.

Soon we were inching our way along a narrow tunnel, the water flowing rapidly beneath our feet. The cave walls closed in around us, as did the ceiling, and soon I was bent double, bumping my head against the ceiling.

A rushing, roaring sound filled our ears and around the corner we encountered our first underground waterfall. Mica shouted instructions, trying to be heard above the din of the rushing water. Her instructions sounded important, outlining how best not to hurt ourselves, but thanks to the waterfall I couldn’t quite hear the detail.

I looked up into a virtual constellation of glow worms. Their cool glow sparkled along the ceiling of the narrow tunnel, making it look exactly like a starry night sky

Turning round, I inched towards the lip of the waterfall, the rubber ring clutched against my back. Then, a jump backwards into the darkness, a momentary free fall and with a huge splash I was bobbing up and down like a hapless cork in the underground river.

The current swirled around my rubber ring and I bumped into my compatriots who were floating nearby. The water was freezing, swiftly soaking through my wetsuit and chilling me to the bone.

But there was no time to concentrate on discomfort as we were off again, whirling down the darkened river, trudging over boulders, crouching around narrow pinch-points in the cave system. Not an experience for the claustrophobic…

Above our heads the first glow worms could be seen, marking their territory on the cave walls with their pale blue glow. Another underground waterfall roared ahead, this one larger, and then a mini white water rapid – all done in complete darkness, save for the dim light from our head lights.

An hour later, we were near the grand finale. With all of us bobbing about in the water in our tubes, we assembled in a long line (dubbed ‘the Human Caterpillar’), clutching the feet of the person in front of us.

Then, as I was in the lead, the guide grabbed my feet and told us all to turn our lights off. As she dragged the lot of us along through the darkness, I looked up into a virtual constellation of glow worms. Their cool glow sparkled along the ceiling of the narrow tunnel, making it look exactly like a starry night sky.

It was breath-taking, and I lay in my tube, teeth chattering with cold but now oblivious to what appeared to be the onset of acute hypothermia as we continued in silence through the darkness, the whirling river waters illuminated as if by moonlight from above.

“OK everyone, this is where you all find your own way out of the cave,” said Mica. “Keep your lights off and follow the glowworms – hopefully we will see you outside.”

Bumping along the tunnel walls, I followed the sparkling trail of glowworms above me and soon the absolute darkness of the cave started to lighten – imperceptibly at first, and then increasing by degrees until I could see the mouth of the cave, and the lush forest beyond.

Emerging from the cave mouth, I looked back as the last of the tubers emerged dripping into the light. Behind them, the darkness loomed, closing in on a secret world of swirling black water and the glowworms that illuminate the abyss with their light.