Helen van Berkel heads underground with her daughter for the stunning delights of Waitomo.

Who knew that a fratricidal cannibal could produce such glowingly beautiful poo? I certainly didn't. But this luminescent constellation hid a terrible secret.

Were I to fly towards to those evilly promising lights, I would find myself caught in a silken but deadly web, my guts sucked out of me, the meal of the seemingly innocent glowworm, the star of Waitomo, the smiling stuffed toy of the gift shop.

Luckily, I'm not one of the unfortunate creatures of the waters that flow through the Ruakuri Cave. I'm one of the human visitors who walk and abseil and bob through on inner tubes.

The Legendary Blackwater Rafting Company. The Waitomo caves experience includes blackwater rafting and abseiling. Photo / Supplied
The Legendary Blackwater Rafting Company. The Waitomo caves experience includes blackwater rafting and abseiling. Photo / Supplied

My daughter and I had decided on a weekend bonding trip. We left school and work early on Friday because bunking off is part of the treat. With great excitement and a cache of jokes (A cave is called a tomo. Why tomo? Oh.) we joined the traffic moving at 10 km/h on the Southern Motorway.

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But when you're Going Away For The Weekend it takes more than a rubbish truck hitting an overbridge to drain the enthusiasm.

And we made the most of everything that was new and exciting, unpacking quickly at the Waitomo Top 10 Holiday Park and going for a walk to check out the neighbourhood attractions: the Huhu cafe and Curly's bar, before tucking in for the night.

We began our adventure on foot. We were the first group of the day to enter the Ruakuri cave, trailling guide Alex, who explained the cave's history as we went. Local Maori have known of these caves for more than 100 years but saw them as the gateway to the underworld.

They named them Ruakuri, after two wild dogs that raced out of one of the cave's entrances and ate the spoils of a hunting trip.

The tour starts as Alex lights up the spiral walkway entrance, layer by layer. It's very dramatic.

We follow the metal pathways, rib-height barriers keeping us from tumbling into the abyss — and from touching any of the structures. Stalactites grow about the length of a thumbnail in a century. All it takes to stop that is the touch of an oily human hand and that's that: millennia wasted.

And nature has had fun here, 65m below the surface, a mad sculptor in water and limestone, forming gargantuan pillars, cave coral and curtains of limestone that ripple out from the walls.

There are short stalactites, thick ones, thin ones, wet ones, dry ones. Each stretches out a dripping point to join the stalagmites eagerly reaching skyward to consummate a bond that will be set in stone forever a few million years from now.

Leaping into the Black Labyrinth of the Ruakuri cave below glow worms and stalactites.Photo / Alex Robertson
Leaping into the Black Labyrinth of the Ruakuri cave below glow worms and stalactites.Photo / Alex Robertson

I've seen the caves before but each visit is as astonishing as the last as Alex's torch beam and the pathway lights (blue for no-photography areas) reveal wonder after wonder in this serene land.

In the distance we hear the roaring rush of a cataract that makes the noise of Niagara. Alex tells us that the waterfall is only about a metre high. My ears don't believe him. In fact, I'm still doubting him when I find myself on its precipice later in the day, preparing to jump into the unknown. Backwards. In the dark.

Wearing a wetsuit, helmet and white goofy boots strapped on, butt jammed in an inner tube is another, much wetter, much more exhilarating way to explore Ruakuri.

The Black Water Rafting Company leads us through the Black Labyrinth, a three-hour journey that begins as we squeeze through a hole in the undergrowth. We carry our tubes between floating in the streams that roar and tumble through narrow-wide-narrow chasms.

Some of the more nervous in the group thought our guide was joking when she said to say hello to the resident eel. She wasn't. He obligingly grinned at the camera for us but luckily, even for the less-nervous, he stayed in his dark pool. And then we had to jump over waterfalls.

The Legendary Blackwater Rafting Company at the Waitomo caves. Photo / Supplied
The Legendary Blackwater Rafting Company at the Waitomo caves. Photo / Supplied

It's frightening, exciting, thrilling and wet — all at the same time. We bob along on the current, not lying back too far or cold water will pour down the back of the wetsuit, but enough to gasp and gape at the spectacular light display above.

The guides (on both trips) explain the lifecycle of arachnocampa luminosa aka the titiwai aka the glowworm: they begin life as one of a cluster of about 100 eggs. The first to hatch eats all its brothers and sisters and then builds a comfy hammock somewhere above water, spins its deadly trap and then lolls about waiting for passing flies, moths and mosquitos to be attracted by the glow from its gut.

The glowworm sucks out its victims' innards and feasts. Then it wraps itself in a chrysalis and emerges with one thing on its mind. Mission accomplished, eggs laid, it dies. And that mesmerising blue light, or bioluminescence? It's created by the creature's waste products.

It's marvellous to see your country through the eyes of foreign visitors. You get to preen with parochial pride and squash a few more vowels as if you single-handedly created these wonders: "Schonlichheit," state the Germans.

"Bellissimo!" gasp the Italians.

"Crikey," drawl the Australians.

And the Kiwi teenager: "Wait, what? That light is poo?"

CHECKLIST


Getting there:

is a three-hour drive from Auckland.

Waitomo Top 10 Holiday Park has a range of accommodation options from tent sites to en suite units.

The Black Water Rafting Company offers a range of activities. Its Black Labyrinth adventure, which suits beginners and takes three hours.