We can just make out the Southern Alps in strobing flashes between warehouses and hoppers, their white peaks almost indistinguishable from the shrouding clouds. Somewhere on the other side is our destination, Greymouth.
Ninety-odd years since it was finished, the railway has become purely a scenic indulgence. You can drive from Christchurch to Greymouth in three hours. The TranzAlpine Express takes four and a half - plus an extra hour in our case because a storm has messed with the signals.
Soon, the train squeaks, creaks and sways out of the city and begins bisecting the patchwork Canterbury plains on a fastidiously straight track. The train's audio commentary reckons this is the most ecologically altered environment in New Zealand.
Once, the plains were covered by podocarp forests, kanuka and moa. Now, stretching to the horizon under a cobalt sky, are crops, paddocks, sprinklers, canals, fences, roads, mansions, barns, factories, sawmills, livestock, rabbits.
"Are we at the mountains yet?" asks Mr Four again, now navigating the rings in Captain America's shield.
Gradually the horizon nears and the fields give way to yellow-tussocked hills, which grow into the Craigieburn Range. As we ascend, the scenery becomes ever more dramatic - peaks get craggier and darker, gorse and broom march unchecked, kereru flap desperately across the valley as if in constant terror of plummeting under their own weight. Even the sheep look rangier.
At one point we slide out of a tunnel and the ground plummets to a bleached river carving around cairns of rock far below. Mist seeps down from a snowy peak and waterfalls plunge unchecked for 100m. A hawk wheels overhead. Rain patters on the windows. Oh yes, we're in the mountains now, Grasshopper.
From here, a series of tunnels emerge into gasp-inducing scenes. The commentary reels off Tolkeinesque names: Deaths Corner, Devils Punchbowl, Deception Valley, Mt Misery, Mt Horrible. Everything we see, it says, is on the move - the mountains are being pushed up, the riverbanks are eroding, rocks and debris are sliding into the rivers and being shunted to sea.
We cross vast wild plateaus and stomach-dropping viaducts, pass abandoned railway settlements and gleaming black coal wagons, stop briefly at an Arthurs Pass naked without snow, bump and squeal through the 8.5km Otira Tunnel, and brave the gusty open carriage while sensible folk huddle inside.
We spot a crane that's tumbled into a river - a reminder this part of the country still resists taming, and of the logistics of maintaining this antique railway.
As the landscape evolves again, we emerge into a New Zealand vastly different from the one we left this morning. Primeval rainforest coats steep hills and the farmland is strewn with rocks and stones, stalked by pukeko and weka, and patched with harakeke-filled swamp and clumped cabbage trees.
There's a sense of abandonment here - tumbling cottages, derelict barns, rusting machinery, fallen fences. Ghostly kahikatea trunks jut out of a lake. We pass the Brunner Mine, which still exhales gas 118 years after its deadly final shift.
As we approach Greymouth, the peeling paint of its modest houses contrasts starkly with the plucked and primped lifestyle blocks across the Main Divide. Here, it seems, the locals don't have the luxury of worrying about aesthetics.
Our destination is announced, like in any mid-sized New Zealand town, with the appearance of a Warehouse and a Countdown. Their ubiquitous branding notwithstanding, there's a sense that we've arrived somewhere very different - not just another coast or even another continental plate, but another continent.
CHECKLIST
Getting there: The TranzAlpine travels from Christchurch to Greymouth and back daily.
Bronwyn Sell travelled with the assistance of Tourism West Coast.
