The limestone wall beside the path is hung with a tapestry of mosses, liverworts and filigree fern fronds in every shade of green. Below the path I see a dark brown river flowing through a narrow gorge that appears to end in a great cavern.
Suddenly the whole scene opens to my view. High overhead is the great vault of a cavern roof, some 30m above the river.
Structures that look like stalactites hang down in a threatening mode, many at the point of releasing their tenuous hold. They are stacks of dissolved calcium carbonate absorbed by mosses.
The structures have the aristocratic title of epitrophic speleothem.
Sculptured rock outcrops decorate the cavern walls, fashioned by nature into weird shapes, some taking on animal and human profiles. I'm standing under a natural stone bridge; the remnant of a giant subterranean cave whose roof has collapsed and been carried away by the river.
I can see sunlight beyond the natural bridge through a patterned silhouette of tree fern fronds and forked tree trunks festooned with bunches of epiphytes. It's a Jurassic Park scene, sans dinosaurs.
I climb a wooden stairway and emerge into bright daylight in a grassy hollow surrounded by half-buried limestone boulders with a likeness to crouching humpbacked dinosaurs and medieval crumbling castles.
Many rock outcrops are deeply grooved like the fluted columns of Greek temples because of the acidic action of CO2-laden water dripping constantly off the foliage of ancient forests. One rock carries the fossilised forms of giant oysters that once flourished in the tidal inlet.
Over millions of years, seabed deposits of calcite from sea shells and the skeletons of expired crustaceans have compacted to create limestone rock, which violent earthquakes have thrust upwards to form new coastal hills. Rain and river erosion has etched out these fantastic shapes on the peaceful pastoral landscape.
Having explored the natural bridge I'm keen to see more of nature's handiwork on this classic back-country road.
Some 5km further on, a sign directs me to the Piripiri Caves. A steep bush track leads up to a gaping hole in the limestone rock. I grope my way down some slippery steps with the aid of torchlight and look out on another huge cavern.
A powerful torch is needed to pick out the detail of the strange distorted shapes suspended on the ceiling. There are delicate crystalline columns, limestone straws, speleothems and even a layer of fossilised oysters decorating this alien world. Far below a mysterious brown stream offers an invitation to explore its unknown depths but there is no safe way down.
Continuing on the highway for a short distance, yet another enticing sign leads me down a descending trail past ferny dells and elfin grottos of the imagination. From an elevated platform I look out on the mighty Marokopa Falls.
The falls are spectacular after heavy rain, plunging 36m across a broad vertical rock face.
I'm viewing them when the Marokopa River is in full flood and the foaming cream and white cascade roaring down the face of the escarpment is a scene that thrills the senses. These falls must rate among the most picturesque in New Zealand.
Pressing on with my western odyssey, I have a sense of being in the middle of nowhere. The roadside scene is constantly changing from dense forest to newly-broken-in pasture, reminiscent of the landscape of early colonial times.
The road enters the Marokopa River valley where clusters of spiky cabbage trees proudly proclaim the iconic status of their species. Then without warning I'm trundling into a delightful coastal settlement alongside a peaceful tidal estuary, dotted with whitebait stands. I'm surprised by the size of the town, given its relative remoteness.
The sight of a general store is welcome after my ramblings in limestone karst country. A toasted sandwich and coffee goes down well as I chat with locals who are popping in on a regular basis on horseback and quad bikes.
Some visit the user-friendly library and the tennis court next to the store. There are no outlets for secret-recipe fried chicken or super-sized burgers in this coastal hideaway and that's just the way the locals like it.
I'm told that in spring, regular as clockwork, tiny native fish called inanga get the urge to swarm up the Marokopa River to spawn. This is when the locals rise early and scramble to form a human reception committee to meet and greet the tasty transparent whitebait.
Driving up the steep road above Marokopa, I pull over at the lookout. A green valley sweeps down to the seaside town, which nestles in a bend in the Marokopa River. Beyond are huge, foam-topped Tasman rollers, a broad black-sand beach and dunes that creep inland, consuming pastureland.
I continue over the hill to Kiritehere Beach where there's nothing but a quiet stream and a fisheries sign outlining catch limits. Down the beach is a cluster of old caravans and sheds on private land.
On the southern headland I find fossilised clams and mussels imbedded in the tidal rocks.
Today, the beach is deserted and seems almost primeval in its splendid isolation.
In the evening I stand on Marokopa beach and watch the sun descend to the western horizon, creating a pathway of golden light across the sea. The sky is painted in a vivid palette of orange and red.
I linger in the solitude of the sands before heading back to the unspoilt natural charm of Waitomo. From Marokopa there is also the option of setting out on another motoring odyssey on coastal roads - south to Awakino or north to Kawhia, Raglan and Port Waikato.
My journey of discovery has had all the hallmarks of a memorable mystery tour through Middle Earth. I have unearthed the secrets of the world above ground and it surely matches the wonders that lie beneath.
FACT FILE
Getting there: Waitomo is a 2-hour drive from Auckland.
Staying there: There is ample accommodation ranging from very comfortable backpackers to the Top 10 Holiday Park and the venerable Waitomo Caves Hotel.
What to see: The Sunset Coast, centred on the tiny settlement of Marokopa, is 50km west of Waitomo on an excellent sealed road. The Mangapohue Natural Bridge track has wheelchair access.
Further information: See waitomo.org.nz.
