As New Zealand hikes go, the trail to Ohau waterfall was short, less than half a mile. It started the way things often do in that part of the world, at a deserted gravel pullout next to a deserted black-cobble beach. A microscopic trail sign pointed up a hill. A small dark path, a mix of packed earth and rock, ran next to a boulder-strewn stream. We began to walk.

The going was flat enough, but within a hundred yards the trail ducked into the thorny and dyspeptic jungle that Kiwis call "the bush." The sun vanished, leaving the world mossy, ferny, Jurassic.