A rare flightless parrot, ancient reptiles and some of the world's largest trees are among the natural wonders to be found in New Zealand’s spectacular landscapes

Windy Potatoes gazed up at the God of the Forest, who loomed back at him disconcertingly. The God was tall, towering 51 metres upwards. The God was wide, at almost 14 metres in girth. The God was also very, very ancient – perhaps as much as 2,000 years old – yet, thankfully, the God was still in excellent health.

Windy Potatoes was reasonably tall himself, and (I'm sure he won't mind me saying this) had a substantial girth of his own. But as far as age and overall mass was concerned, he was operating on a very human scale, whereas the God of the Forest was subject to far grander natural rhythms. On the other hand, at that particular moment Windy Potatoes and the God of the Forest were probably thinking much the same thing. And I, feeling the first heavy droplets on my face, couldn't help but agree with them.

"Mate," said Windy Potatoes. "We're about to get very wet."

Windy Potatoes is not his real name. Tawhiri Riwai is a Maori guide whom I'd met in Waipoua Forest, which lies in New Zealand's Northland region – the furthest tip of the North Island. Having translated his name into English for me with a rueful shrug, he then described the significance of the God, who also goes by another name in Maori: that of Tane Mahuta. (The son of Rangi-Nui and Papa-tu-a-Nuku, the sky father and earth mother, Tane Mahuta apparently prised his parents apart to bring light and order to the world.) Then, after a solemn karakia, or prayer, Riwai took me off to see the God of the Forest for myself – at which point the skies opened up and we all got utterly drenched.

A decent slosh of rain has done wonders for the local plants. Tane Mahuta is in fact the largest remaining example of New Zealand's ancient kauri trees, and it, or rather he, rises near the centre of Waipoua, a sub-tropical rainforest. Slow-growing, reaching immense heights and ages, these giants were once found throughout the northern part of the country. However, their strong, flexible timber meant that they were particularly prized by European settlers, who swiftly set about chopping down as many as possible and turning them into boats, houses and furniture.

Quietly getting on with the business of growing steadily upwards for a couple of millennia and then being unexpectedly transformed into a bedside table doesn't seem like a very dignified life-cycle for these behemoths. The Kauri Museum at Matakohe, just to the south, explains things from a human perspective: the harshness of life for people here 150 years ago, and the range of products created from the wood and gum. Finally, of course, there was the dawning realisation that chopping down plants that take three or four centuries to reach maturity was never going to be a sustainable endeavour. As Louise Nowell from the museum explained: "These trees are entire ecosystems. They're like cities up there. The number of birds and plants living on them is phenomenal." A replica sawmill inside the building helps tell the kauri story, alongside an exhibition of kauri gum.

When the trees had been cleared, the settlers set about farming instead. Waipoua Forest remained, largely because of the impracticalities of removing wood from the local terrain. An 18-mile stretch of road twists and wiggles through what is now a national park, passing between the huge pale-barked kauri, which loom over mamaku ferns and low-lying scrub. From a vantage point above the treetops, the greenery seems to stretch forever, undulating towards the horizon. But Waipoua Forest is a kind of island now, marooned in a modern landscape of sheep farms, pretty roads and tidy homesteads.

Click here to watch Ben Ross’ video of Milford Sound

New Zealand's island ecology – from the kauri trees to the kiwi, the country's emblematic bird – is unique. Twenty years ago, Douglas Adams – the man behind the comedy science-fiction epic The Hitchhiker's Guide to the Galaxy – arrived with naturalist Mark Carwardine. The writer was intrigued by the peculiarities of the birdlife. With no cats, dogs, ferrets, or other mammalian land predators, there was little for the birds to fear, so many lost the use of their wings.

"There is," wrote Adams in his book, Last Chance to See, "a trade-off between flying and eating. The more you eat the harder it is to fly. So increasingly what happened was that instead of having just a light snack and then flying off, the birds would settle in for a rather larger meal and go for a waddle afterwards instead."

Adams and Carwardine were searching for some of the world's most endangered species. Among them was the kakapo, which according to Carwardine, is "the world's largest, fattest and least-able-to-fly parrot" and was once widespread throughout New Zealand. Now critically endangered by the arrival of dogs, ferrets and weasels, the species is confined to a pair of New Zealand's offshore islands that have been cleared of predators.

Douglas Adams suffered a fatal heart attack in 2001, aged just 49. But his affection and concern for New Zealand's strange wildlife is celebrated in the Last Chance to See television series currently being broadcast on BBC2, in which Carwardine and Stephen Fry take up the kakapo's tale. But you don't have to be a polymathic national treasure or a naturalist to appreciate New Zealand's flora and fauna. You do, however, have to be patient.

My first attempt at kiwi spotting was, frankly, a wash out. I'd hoped to see them in the Trounson Kauri Park, a protected area just to the south of Waipoua. But kiwi are elusive, nocturnal, and they don't like getting wet. I took shelter instead at Waipoua Lodge, a beautiful wooden farmstead on the edge of the forest, which boasts four vast suites carved from old farm buildings. Surrounded by such colonial luxury it was hard to think that trudging through the woods as the rain lashed down outside would be a good idea. The kiwi probably thought the same.

I tried again in Wellington, New Zealand's gracious capital city. Here "Zealandia – The Karori Sanctuary Experience" is an ingenious attempt to recreate the wildlife of New Zealand "the day before humans arrived". A 550-acre section of valley enclosing the city's old reservoir has been fenced off and cleared of all predators, and around 30 native bird species have beenV C introduced to the area, including the little spotted kiwi, a variety previously extinct on the mainland.

It's almost entirely un-zoo-like, in that there are no guarantees that you will see anything at all. Nevertheless, I was optimistic as I arrived for my nocturnal encounter. My guide Matt Robertson pointed out a twinkling wall of glow worms, a tuatara (a native reptile that gives every appearance of being a lizard, but apparently is not one) and a species of insect called the cave weta. It felt eerily primeval as we shone our torches into the gloom, and although we didn't see any kiwi, we did hear one calling. It was a sound that, as Robertson said, "has not been heard in these parts for over a hundred years".

Click here to watch Ben Ross’ video of Sirocco the kakapo

I gave up on kiwi at that point: there was, after all, plenty more birdlife to look out for, much of it available during daylight hours. Somes Island, known as Matiu in Maori, lies a short boat ride from Wellington harbour. Once used as a quarantine for human immigrants, then for cattle, it is now an easily accessible nature reserve. Upon arrival I met warden Matt Sidaway and Reg Cotter, a local guide whose enthusiasm for the local wildlife extends to creating nesting boxes for the world's smallest penguin, the little blue.

First I was asked to check my pack for rogue mice. ("It's like customs for us," said Sidaway. "Without biosecurity the risks would be too high.") Then I was swiftly introduced to the endangered red-crowned parakeet as it flitted past, to the giant weta (a bigger, badder version of the cave weta) and, more appealingly, to a little blue penguin, its skin iridescent, its manner grumpy. From the summit of the island, the view back into Wellington – ringed by rippling peaks – was spectacular.

Later, back in the city, I visited the extraordinary Te Papa ("Our Place") museum, a vast modern building – all wonky corners and diagonals – which sits at the Wellington harbourside. Inside is a bold attempt to sum up the history of New Zealand – its geology, its wildlife and the interplay of Maori and European cultures – via a series of intriguing interactive displays. The sheer pride that New Zealand takes in itself bulges out from the place, as well as a breathless feeling that anything the locals come up against will eventually be sorted by good old kiwi know-how.

It's that sort of grit that keeps the kakapo, or "night parrot", from tottering into extinction. When Adams and Carwardine first visited New Zealand there were around 40 left. Largely thanks to the efforts of the Department of Conservation – often referred to as "Doc" by New Zealanders – there are now 125 of them, with the majority on Codfish Island, near Stewart Island, at the southern limit of New Zealand. Although Fry and Carwardine were granted access to film their programme, tourists aren't allowed to visit Codfish Island, which means kakapo sightings are hard to come by. Happily a bird called Sirocco is occasionally brought slightly nearer to human habitation for kakapo-consciousness-raising purposes. And last Saturday he welcomed his first guests of the season to Ulva Island.

From Invercargill, New Zealand's southernmost city, I reached Stewart Island via what was – for me – a nail-biting flight jammed into a 10-seater light aircraft. The local passengers seemed to think nothing of the buffeted plane, the churning seas or the grey clouds scudding over the Foveaux Strait, but I was extremely thankful to see the air-strip splashed over the top of a welcoming hill. Below lay the small town of Oban, home to most of Stewart Island's 380 inhabitants.

Stewart Island, or Rakiura in Maori, is New Zealand's third-largest island, yet it is still tiny: a chunk of lush greenery set to the south of the South Island. It was once used as a base for logging and sealing, and is now almost entirely given over to luxuriant national park.

In a community this size, people tend to double up: Ian and Philippa Wilson run Port of Call, a smart B&B with views out over the bay; and Ian ferries tourists over to Ulva Island, the sanctuary that lies at the heart of the nearby Paterson inlet. "It's certainly a lot easier living here now," said Wilson as he showed me round. "But it's still a place where time stands still."

On tiny Ulva Island time has been reversed. Here, among the local birds are others that have died out on the mainland and been reintroduced. On an hour's walk round its well-marked paths, I saw the predatory, flightless weka stalking the shore, and glimpsed the deep red plummage of the kaka, New Zealand's forest parrot. The rare Stewart Island robin hopped up dutifully and posed for pictures – and there might be only 700 of the red-flashed South Island saddleback still in existence, but several of them were flitting around at the shore. At Boulder Beach, the dense bush gave way to a rugged stretch of sand; the view back down the inlet revealed pristine swathes of dark green.

And then as night fell I finally met Sirocco the kakapo. When I first read about these birds 20 years ago, it didn't seem at all likely that they'd still be around in 2009. About two-feet long, nocturnal, with a bizarre mating pattern to do with the flowering of the local rimu tree, kakapo also have a habit of standing still rather than running away from predators. In short, they seem just a little too weird to thrive. But they have – if not thrived – at least clung on. Twelve-year-old Sirocco was hand-reared and therefore tolerant of humans. On Ulva, he lives in two pens – one large enough for him to forage in, and another, ringed in perspex, where visitors can see him.

We stood quietly in the gathering gloom. Then, with surprising speed, there he was, climbing up a log and looking solemnly out through the clear plastic. Jo Ledington from the Kakapo Recovery Programme later explained that he was an "advocate" bird: by showing him off in public, the programme hoped to raise public awareness.

He raised my awareness by eating grapes from her hand and looking out at me – as huge and parroty as I'd imagined, with a bit of owl thrown in. The creamy whiskers below his chin contrasted nicely, I thought, with the green and brown of his plumage. We examined each other for half an hour or so – me with a sense of wonder and delight, Sirocco with a sort of alert indifference. Then it was time for him to get on with his day, and for me to go to Oban's lively South Sea Hotel for a few celebratory glasses of Speight's Gold Medal Ale.

Home for the kakapo was once New Zealand's Fiordland, a region where immense folds of glacier-scarred granite rise from the ground like mouthfuls of teeth. From Stewart Island, I flew in another tiny plane to the majestic World Heritage Site of Milford Sound, an utterly beautiful 15km-long fiord on the coast. On a cruise along its length I saw fur seals and tiny penguins frolic as the sun finally hit its stride and lit the scene in glitter. It's the sort of scenery where, Douglas Adams wrote, "One's first impulse, standing on a cliff top surveying it all, is simply to burst into spontaneous applause."

Sirocco's enclosure might be a little less dramatic than his native Fiordland, but the fact that he's around at all is pretty impressive in itself. One of Adams's odder science-fiction inventions was a psychological torture device called the Total Perspective Vortex. According to Adams, "When you are put into the Vortex you are given just one momentary glimpse of the entire unimaginable infinity of creation, and somewhere in it a tiny little mark, a microscopic dot on a microscopic dot, which says, 'You are here.'" Spare a thought, then, for Sirocco, as he potters around his pen on tiny Ulva Island, off Stewart Island, near the South Island of New Zealand, in the middle of the Pacific Ocean. He seems to be bearing up remarkably well, given the circumstances.

Travel essentials: New Zealand

Getting there and getting around

* Air New Zealand ( 0800 028 4149; airnewzealand.co.uk ) provides the only direct flights from the UK to New Zealand, flying daily from Heathrow via Los Angeles to Auckland and five times a week via Hong Kong. Visitors travelling via Los Angeles need to complete the Electronic System for Travel Authorisation (Esta) at least 72 hours before travel ( usembassy.org.uk ). Air New Zealand also has an efficient network of 26 domestic connections within New Zealand.

* Stewart Island Flights (00 64 3 218 9129; stewartislandflights.co.nz ) operates light aircraft from Invercargill to Oban three times daily and will fly from Invercargill to the airstrip at Milford Sound by arrangement.

Staying there

* Waipoua Lodge, State Highway 12, Waipoua Forest, Northland (00 64 9 439 0422; waipoualodge.co.nz). Doubles from NZ$490 (£222) including breakfast.

* Museum Hotel, 90 Cable Street, Wellington (00 64 4 802 8900; museumhotel.co.nz). Doubles from NZ$225 (£102) including breakfast.

* Port of Call, PO Box 143, Stewart Island (00 64 3 219 1394; portofcall.co.nz). Double room from NZ$385 (£175) including breakfast (minimum two-night stay).

Visiting there

* Footprints Waipoua (00 64 9 405 8207; footprintswaipoua.co.nz) offers Maori-guided tours of Waipoua forest. A 40-minute visit to Tane Mahuta costs NZ$15 (£6.80) per person.

* Kauri Museum, 5 Church Road, RD 1, Matakohe, Northland (00 64 9 431 7417; kaurimuseum.com). Open daily 9am-5pm, admission NZ$15 (£6.80)

*Zealandia – The Karori Sanctuary Experience, Waiapu Road, Wellington (00 64 4 920 9200; visitzealandia.com). Open 10am-5pm daily, admission NZ$14 (£6.30). Night tours last two hours and cost NZ$60 (£27).

* Somes/Matiu Island is reached via the Dominion Post Ferry (00 64 4 499 1282; eastbywest.co.nz ) which departs three times daily from Wellington's waterfront. Returns are NZ$21 (£9.50) Access to the island is free. The visitor centre is open from 8.30am-5pm.

* Museum of New Zealand Te Papa Tongarewa, PO Box 467, Cable St, Wellington (00 64 4 381 7000; tepapa.govt.nz ). Open 10am-6pm daily (10am-9pm Thursdays). Admission free.

* Sirocco the kakapo is on Ulva Island until 26 October. Tickets are NZ$90 (£41) per adult, including transfer by water taxi from Stewart Island. For details, see kakapoencounter.org .

* Real Journeys (00 64 3 249 7416; realjourneys.co.nz ) offers overnight cruises onboard the Milford Mariner from NZ$329 (£150) per person, based on two sharing, including activities, dinner and breakfast.

More information

* Tourism New Zealand: newzealand.com

Peaks and beaks: Mark Carwardine

I first visited the land of the kiwi in 1989 with the late Douglas Adams, as part of a round-the-world tour in search of endangered species. We went to look for the kakapo – a large nocturnal parrot that smells like a musty clarinet case and has a song like an unreleased collection of Pink Floyd studio outtakes.

The kakapo is exactly the kind of bird that makes it worth flying to the other side of the world to see. In fact, I've just been back to see it all over again – this time with Stephen Fry for the BBC series Last Chance to See – to retrace the steps Douglas and I took exactly 20 years before.

We spent several weeks filming in New Zealand but three days, in particular, stand out in my mind. The first was a stop to see a distant relative of the kakapo, a notorious mountain-dwelling parrot called the kea. Keas tend to loiter around public places, partly because these offer an easy source of junk food and partly because that's where they can get up to most mischief.

We went to see them at a car park by the entrance to the Homer Tunnel near Queenstown. One of the birds stole a man's baseball cap and was chased across the car park by its rightful owner. We laughed uncontrollably as the other birds just turned away, looking about as innocent as juvenile delinquents caught smoking behind the bike shed.

I also enjoyed a visit to the Chatham Islands, a tiny archipelago slap-bang on the international dateline some 500 miles east of mainland New Zealand, where we went to see a rather unremarkable little bird called the Chatham Island black robin.

The black robin came closer to extinction (without actually vanishing altogether) than any other animal on the planet. At one point, in 1980, there was just a single breeding pair left. But thanks to a dramatic rescue operation there are now 250... and counting. For me, as a naturalist, I was more excited about meeting this famous little bird than I would have been about meeting a Hollywood star. Sad, I know.

The third and most memorable highlight was a day spent exploring Fiordland, a breathtaking tract of mountainous terrain in the south-west corner of South Island. We did it from one of those little helicopters with a bubble cockpit. We circled rugged peaks reaching high into fluffy white clouds, swooped along green valleys, hovered in front of thunderous waterfalls, and marvelled at the sheer splendour of it all.

Stephen and I were still engrossed in the surreal world around us when our pilot plugged his iPod into a socket on the helicopter's control panel and, rather appropriately, Pink Floyd's Dark Side of the Moon erupted into our headsets. Suddenly, we were in an imaginary spacecraft, wheeling and turning over a fantasy make-believe world. That was a highlight neither of us will ever forget.

The New Zealand episode of Last Chance to See is on BBC2 tomorrow at 8pm.