Mount Owen (New Zealand)

Where it sits. Mount Owen rises to 1,875 metres at the southern end of Kahurangi National Park in the Tasman District, between Murchison and the Nelson lakes country. It is the high point of the Owen Range, and from a distance it looks like an ordinary bulky alpine massif. Up close it is nothing of the kind. The summit plateau is a field of exposed marble — Ordovician limestone metamorphosed into hard crystalline rock and then dissolved by two hundred million years of rain into a landscape of fluted blades, ribs, blocks, natural arches and open shafts. Geologists call the fluting karren; walkers call it the ice-rink, the crevasse field or worse. There is no soil across large parts of it, no vegetation to speak of, and no reliable line across.

The largest cave system in the country. Beneath the plateau is Bulmer Cavern, the longest cave system in New Zealand with well over seventy kilometres of surveyed passage and a vertical range of several hundred metres, explored progressively since the 1980s by expedition caving teams. Water that falls on the summit disappears into the rock almost immediately and re-emerges far below at resurgences on the mountain's flanks, most spectacularly at Blue Creek near Courthouse Flat, where extraordinarily clear water comes out of the base of the hill in volume. The marble here is the same Arthur Marble that outcrops on Tākaka Hill and Mount Arthur further north, and this belt is the most extensive marble karst in New Zealand. It is also fragile: the sculpted surfaces take millennia to form and boot damage does not repair.

On screen. Mount Owen's marble pavement was Dimrill Dale — the shattered stony ground on the eastern side of the Misty Mountains where the Fellowship emerges from the eastern gate of Moria after Gandalf's fall, and where Aragorn drives them on toward Lothlórien. It is one of the very few Middle-earth locations that needed almost no dressing at all: the grey blades and clefts of the karst read as broken mountain rubble without any set construction, and the natural voids and arches supplied the sense of a country undermined by something. The unit reached it by helicopter, which is essentially the only practical way to put people and equipment on that plateau. The summit block also appears in The Hobbit, and the wider Owen and Arthur ranges provided further alpine plates.

What you actually see today. Marble, in every direction, weathered to a pale grey that goes almost white in flat light and takes shadow beautifully in the low sun. Between the ribs are grikes — deep, narrow, straight-sided fissures — and scattered across the plateau are shafts that drop out of sight. Alpine plants cling in the pockets where a little soil has collected, including some species restricted to this karst. Kea are present and confident. In fine weather the view runs from the Nelson lakes to the Tasman Mountains and out toward the West Coast. In cloud the plateau is genuinely dangerous, because there are no landmarks, the compass work is complicated by broken ground, and the holes do not announce themselves.

A park that came late. Kahurangi National Park, which contains the mountain, was only gazetted in 1996, making it one of New Zealand's newest and, at roughly 4,500 square kilometres, its second largest. It protects an unusually old and unusually diverse piece of country: the northwest of the South Island escaped the worst of the Pleistocene glaciation, so plant lineages survived here that were wiped out further south, and the park holds more of New Zealand's native plant species than any other. Great spotted kiwi are widespread in the beech forest, and giant land snails of the genus Powelliphanta, carnivorous and slow-breeding, live on the damp forest floor.

Getting there — and being honest about it. This is not a location you drive to, and it is not a day walk. The standard route starts at Courthouse Flat near the Owen River, off State Highway 6 about half an hour east of Murchison, on an unsealed road. From there a track climbs through beech to Granity Pass Hut, a basic Department of Conservation hut, in roughly four to six hours. The route from the hut onto the plateau and toward the summit is marked with poles and cairns in its lower sections but becomes route-finding across karst higher up, and it takes several more hours each way. In practice Mount Owen is a two- to three-day trip for fit and experienced trampers with navigation skills, and it should not be attempted in poor visibility. Snow lies on the tops well into December and conceals the shafts, which is the single most serious hazard on the mountain. Helicopter charters operate out of Murchison and Nelson for those who want to see the plateau without the tramp, weather permitting, and that is a legitimate option rather than a shortcut. Carry all water; the mountain drains straight through.