Cave Stream

Where it sits. Cave Stream — also recorded as Broken River Cave — lies in the Castle Hill basin of inland Canterbury, directly beside State Highway 73 between Springfield and Arthur's Pass. The signposted reserve car park is about 100 kilometres from Christchurch and 40 kilometres short of Arthur's Pass village, in open tussock country at roughly 700 metres above sea level, with the Craigieburn Range on one side and the Torlesse on the other. The stream runs across the flats, disappears into a limestone bluff, travels 594 metres underground, and re-emerges downstream in a small gorge. Both entrances are within a fifteen-minute walk of the car park, which makes this one of the few caves in New Zealand that ordinary travellers can pass through end to end without a guide, a ladder or a rope.

The story behind it. The cave is cut into the same Oligocene limestone that forms the tors of the surrounding basin, rock built from the shells and skeletons of marine organisms when this part of Canterbury lay beneath a shallow sea roughly 25 million years ago. Uplift along the alpine ranges raised the beds, and slightly acidic surface water did the rest, dissolving joints into a single main passage. Ngāi Tahu knew this basin as a seasonal travelling and food-gathering route between the Canterbury plains and the West Coast greenstone trails, and the charcoal rock drawings at Kura Tāwhiti a few kilometres south are part of the same cultural landscape. The cave and its surrounds are protected as the Cave Stream Scenic Reserve, administered by the Department of Conservation, and the site has been a fixture of Canterbury school trips and tramping-club outings for generations.

Doing the through-trip. The accepted direction is upstream, entering at the lower resurgence and walking against the current to the upper entrance, so that anyone who turns back is carried out by the flow rather than pushed deeper. The passage is mostly walkable in knee- to thigh-deep water, with a few narrow sections and one short waterfall near the upstream end that is climbed on fixed bolts and chain. The trip takes most people between thirty and forty-five minutes. The water sits close to single-digit temperatures year round, the passage is entirely dark, and the exit at the top involves a scramble onto a ledge above the stream.

A serious place, plainly. Two people have died here — one by drowning, one from hypothermia — and the cave floods without warning after rain or during the spring thaw. The Department of Conservation posts flow warnings at the entrance, and the sensible rules are simple: never enter alone, carry at least two working head torches per person, wear warm synthetic layers and sturdy footwear rather than sandals, and turn around if the water is discoloured, pushy or above thigh height. Rain falling in the headwaters can raise the level long before it reaches the flats, so a clear sky at the car park is not a guarantee. Groups with children should treat it as a technical trip rather than a walk.

What else is in the basin. The reserve sits in the middle of one of the South Island's most concentrated pockets of interest. The limestone tors of Kura Tāwhiti / Castle Hill, free to enter and among the country's best-known bouldering grounds, are five minutes south by car. Flock Hill station, where the climactic battle of The Chronicles of Narnia: The Lion, the Witch and the Wardrobe was filmed in late 2004, lies immediately north — indeed the station took its name from the boulders near Cave Stream, which the runholder thought resembled flocks of stone sheep. Cave Stream itself was not a film location, a distinction worth making because tour listings often blur the two. Lake Pearson, the Craigieburn beech forest tracks and four club skifields are all within twenty minutes.

Getting there and timing. The reserve is reached only by road; the highway is sealed and open year round, with chains occasionally required in winter. There is a gravel car park, an information shelter and a toilet, but no shop, no fuel and no mobile coverage in parts of the basin — the nearest services are at Springfield to the east or Arthur's Pass to the west. Late summer and early autumn, from January to April, bring the lowest and clearest flows. Spring is the least suitable season because snowmelt swells the stream. Bring a full change of dry clothing for afterwards; there is nowhere sheltered to warm up, and the wind across the flats is often colder than the cave.