South-west New Zealand is the wettest, wildest quarter of the country, and Te Wahipounamu, which in Māori means the place of greenstone, is its official name. The World Heritage area stretches over about two and a half million hectares and takes in four national parks: Fiordland, Mount Aspiring, Aoraki Mount Cook and Westland Tai Poutini.
Fiordland is what happens when glaciers cut into mountains and the sea fills the result. Steep granite walls rise straight out of the water, hung with waterfalls after rain, and the forest clings to rock so thin that after heavy storms whole slopes of trees slide into the fiords in great scars. Rain is the rule. Parts of the district get more than six metres a year, and when it falls the waterfalls multiply into hundreds. When the sun appears, the effect is almost too bright to bear.
For the rider, the nearest real road is the Milford Road, which runs from Te Anau up the Eglinton valley, past Mirror Lakes and the Divide, and through the Homer Tunnel, a 1.2-kilometre bore that passes under the mountains to the Cleddau valley. The road is spectacular and demanding: narrow in places, steep descents on the far side, wet surfaces, and an avalanche risk in winter and spring that can close it without warning. Check conditions before you leave and carry rain gear, a warm layer and a charged phone. Cold air at the tunnel can surprise even in summer.
Fuel matters. Te Anau is the last proper stop for petrol, and Milford has none, so fill up before the long run. Queenstown is a long way back. Sandflies thrive in this country, so insect repellent is as important as anything in your bag, and keas, the mountain parrots, will pick at bike seats and luggage straps if left alone.
Go in a spell of settled weather in summer, start early, and do not expect to complete the day's plan if the rain closes in.