You get few opportunities in life to experience absolute darkness. No crack of light under the door, no stars above, no chance of your eyes adjusting. The kind of darkness where you have to put your hand over your face and feel your lashes flicker to be certain your eyes are open.
We find this darkness 70m under solid limestone in the Nile River cave system at Charleston, southwest of Westport. One by one, we switch off our miner's lamps, keeping a tight hold on the kids in case they freak.
When the last light goes off, you can almost hear your eyes whirring, like an automatic camera lens trying to focus. Everyone falls silent. The cold seeps through our clothes. I'm grateful to be holding something solid, even if it's the shoulders of a 7-year-old boy.
Our caving guide, Mark James of Norwest Adventures, reckons you'd go cave crazy after 10 minutes of this — and he's tried it. Your ears overcompensate, and you hear — or think you hear — all sorts of things that can't be explained by the water that has carved these caves out of the limestone over a quarter of a million years.
Even once we switch on the lights, the caves remain spooky. They're still as death. With little airflow in most of the system, it can take a week for a drop of water to collect and fall, and a footprint can last 1000 years. In a roped-off area, a set of dog prints head off through the dust. They are 55 years old, made by the long-dead pooch of the man who first explored these caves. And you really don't want to think about how many tonnes of rock is propped above your head, or how those cow-sized boulders came to be piled up like that.
Shadows creep and grow behind milky white stalactites and stalagmites. One cave looks like a dusty graveyard, the stalagmites forming dozens of tombstones. Many of the caves have names — the Room of Chaos, the Hall of the Refugees, Giraffe Corner. There's an altar-like formation where a couple of German tourists were married.
The calcified formations, created drip by drip over many thousands of years, start to resemble familiar objects: an elephant, a tiered wedding cake, cauliflower with drizzled cheese sauce, a giant jellyfish with tentacles, Davy Jones with dreadlocks of folded calcite, a Buddha complete with fine eyelids and ears, cracked lips and even nose hairs.
And then there's claustrophobia, of course. Though some of the caves have soaring roofs or give you the sense of standing in the yawning ribcage of a giant whale, in other places even the 5-year-old has to duck.
It's a breath of fresh air when the cave opens out to a soaring natural hall. A keyhole in the stone roof lets in a trickle of water, falling into a pool below. Beams of sunlight pick up individual droplets, throw into relief the ridges and shadows in the ceiling, and light up a rainbow in the mist. A gaping hole in the cave wall reveals a slice of primeval bush, its rich green reflected in the still water. The hall has that foresty smell of life and decay, absent from the dry air of the caves.
We duck around a corner and switch off our lights. As our eyes adjust, we notice pinpricks of light above our heads. A few at first, then dozens, then thousands. A galaxy of glow worms, their silvery threads hanging to within inches of our faces.
We retrace our steps to the cave entrance, where we emerge, blinking, into blessed air and space.
We climb down a staircase built into a cliff and cross a suspension bridge, then take a small train through a rainforest of kahikatea and ferns that served as a setting for the BBC TV productions The Lost World and Walking with Dinosaurs.
Beside us, the Nile River tumbles, its water green with tannins.
A hundred metres above, a limestone cliff juts out like a ship's bow, as if showing us the way back from the ancient world to civilisation (aka Charleston, pop 276). Above the canyon, a crisp blue sky makes us feel like we can see forever — and never have we been more grateful for that.
Getting there: Sounds Air flies between Wesport and Wellington up to 26 times per week.
Details: The Charleston Glow Worm Cave Tour is one of several caving experiences run by Norwest Adventures.