Chattering kakariki and swooping kaka skim tree tops under the watchful eyes of fat kereru and herons. The forest looks so ancient you half expect a brontosaurus' head to pop up over the leaf canopy.
Everything is a shade of pounamu - from the deep, dark water that reflects the towering rimu to the lighter green fern canopy underneath.
It is probably the sealed roads that best show how weakly humans have encroached. The 1746sq km island has just 25km of them, all bunched up around the tiny settlement of Oban. Usually the only way to travel further is to don hiking boots and walk the long, ranger-cleared tracks between mountains and forests.
But one or two times a year, 30 or 40 lucky people catch a tour boat to the remote bays on the more sheltered side of the island.
This year I am one of the lucky ones - I have five days living on a converted fishing boat, each night anchored in a different inlet.
After meeting my fellow passengers, I think it fair to say the island is a destination many people save for later in life. Boarding the bus that would take me to the boat trip at Bluff, I was told I would be "much the youngest" of the 38-odd passengers.
"In fact, dear, you'll be bringing the average age down by about 20 years," laughed my neighbour.
Each day we dipped into a new bay and walked an hour or two to see rocks, beaches, mountain moors and different kinds of forest; before returning to the boat to be warmed, fed and watered.
These days most of the island is protected as Rakiura National Park. Trees and birds rule the roost, as they probably have for millions of years. Here and there we saw a remnant of a failed human settlement - the skeleton of a whaling station, maybe, or the scraps from an old ship-building yard.
Oban (population 400) is the only surviving township; made up of fishermen's homes, holiday homes for Southlanders and a bit of tourist accommodation. The holiday homes make me chuckle - surely only Southlanders would holiday somewhere this chilly.
One day, we have lifejacket drill. The next day Ron - our guide, who lived on the island for 35 years and was a search and rescue volunteer - tells us what the jackets are for.
"It's so we can pluck the right number of bodies from the water."
He tells us no one would survive long in the sea.
It wouldn't be true to say the island is unchanged by people. Rats have invaded, stealing birds' eggs and driving out shy, native parrots, and deer were introduced to give sport to hunters.
We visit Oyster Bay and learn the last oyster left in a jar bound for Sydney circa 1838. About the same time blue whales were reduced to almost nothing - slaughtered in just over three years using the effective, if short-sighted, tactic of killing the calf so its mother would follow the boat to shore to be killed.
On the bright side, conservation rangers moved kiwi, kakapo, weka, saddlebacks and rare black and white Stewart Island robins to two smaller islands out of the reach of rats - in the nick of time, as it turned out - and many thrive there as they do nowhere else in the world.
One of the sanctuaries is open to visitors while the other, the safety net, is for birds alone.
I am looking the wrong way the day someone spots a kiwi. But a gang of sea lions decides to make it up to me before I can even feel disappointed. Just as we are zooming ashore to look for their colony on the small tin dinghy we use to get about, a dozen of them decided to come out and meet us.
Their sleek bodies dive and circle around us, seeming as curious about us as we were about them. The females flash us their creamy tummies and, in one instant, four whiskered snouts rise from the water in a line, less than a metre from the boat. Our cameras flash, but the line of smooth heads refuse to be caught on film.
At Port Pegasus, we go to shore and then leap straight off into the undergrowth. The track is only visible once we are below the upper canopy of bush, but those waiting to jump can track the progress of those in front by watching the tree tops rustle in a line up the slope.
Another day we slither off the dinghy on to slippery rocks, a chain of human hands making sure nobody lands on their rear. There is a head-count every time we go back the boat, and one day I am glad the guides check. The wind is so strong on a spectacular rocky outcrop I fear my oversized waterproof pants will carry me away. Two days earlier it might have been lift-off but, thanks to on-board chef John, we have been eating delicious comfort food and my feet stay on the ground.
On the final morning, the boat drops us at the island's main port so we can walk over the hill and see Oban. Mist is crowning the island in its characteristic mix of drizzle and rainbows and, as the sun rises from behind the clouds, a rainbow arches over the island. It is the perfect sight to end a misty, lovely and often cold week.
Now that modern tourism offers hot food and hot showers, the grey chill is part of the island's charm. After all, if the weather was nicer, there might be nothing left to see.
CHECKLIST
Real Journeys operates its Discovery Cruises to Fiordland and Stewart Island during May-September 2010. To find out more freephone 0800 626276.
Eloise Gibson cruised around Stewart Island as guest of Real Journeys.
