The distance from the helicopter to the lodge looks a good 20-second dash, hindered as I am by heavy camera equipment and a bone-numbing lethargy produced by a biting wind chilling the thermometer to -20C.
It's a fair bet that if there are polar bears close they will pounce and rip me to shreds in seconds. This would do much to put Churchill, one of Canada's most remote towns, on the global map, although not for the reasons its inhabitants would like.
For Churchill describes itself as the polar bear capital of the world, and if it wasn't for the bears it would struggle to exist. The town is a testament to the way eco-tourism is now big business, a force for regeneration. In October, Canada's bears start their migration north into the Arctic, where they devour seals with abandon and nearly double their body weight. Situated on the south-western edge of the mighty Hudson Bay, the town lies slap bang in the path of the bears as they head for colder climes.
The huge mammals can move at more than 30 mph, even those that weigh more than 1,000lb (70 stone) and stand 12ft tall on their back legs. They look semi-comatose, the result of having not eaten for months, but the merest whiff of food will send them charging across the ice.
The pilot told me shortly before we took off for the lodge: 'Run straight from the 'copter to the lodge. I have a gun.' This is vaguely reassuring and extremely thrilling. As I peg it across the frozen tundra that borders Hudson Bay I feel my guide's gun trained on the middle distance, ready to pick off a bear in a flash. Another guide, armed with a shotgun, rushes out to meet me. Bravely I rush past him and into the warm confines of a brothel.
Actually, it's no longer a knocking shop. The White Whale lodge, one of Churchill's oldest buildings, was a house of ill repute until the Thirties. For decades it served the navvies and stevedores who worked on the railway and in the deep-water port in this small, inhospitable town (population 1,000 in a good month), which made most of its money by exporting wheat to Europe.
Today the brothel is a wildlife lodge, protected by sturdy bars which form an encapsulating cage, keeping the humans in and the bears out, a sort of inverse zoo. There is something surreal about eating piping-hot spaghetti bolognese and sipping fine British Columbian red while a frustrated man-eater eyes you hungrily less than 2ft away.
These days the railway still runs - three times a week - but the port is not so busy. The massive shipments of wheat are not so regular and there is speculation that one day the port may close altogether. The huge US Army base disappeared in the Eighties, leaving only Canada's second longest runway and a motley collection of prefabs as a legacy.
You cannot reach the town by car. Most people who make the journey come by plane from Winnipeg in the south of Manitoba, a three-hour trip. Winnipeg itself is almost three hours from Toronto. Churchill is not a place you stumble across. Many of the town's inhabitants have travelled no more than 50 miles away in their lives.
So thank heavens for the bears, without whom Churchill would almost certainly fold. Actually, it's more than just the bears which pull in the punters. In the summer - when the temperature has been known to hit a heady 22C - Churchill is home to hundreds of beluga whales and copious varieties of birdlife. Fishing is said to be good, too, attracting anglers from far and wide. Tasting the local salmon (completely different from the chemically bloated protein we get in Britain) suggests this alone makes the pilgrimage worth the effort.
There is also the Aurora Borealis, or northern lights as it is more prosaically known to tourists. This natural phenomenon is particularly popular among Japanese honeymooners who like to consummate their marriages out on the tundra under the Aurora, in the belief that this will make their offspring grow up to be healthy, wealthy and wise. Probably with great teeth to boot.
No one is quite sure where this 'Eskimo' myth originated, although someone suggested its provenance dates back to an early episode of Northern Exposure which carried a similar plot line and went down well in the land of the rising sun.
But it is the bears that really draw the crowds. As the bay freezes and the water coagulates, it forms huge slabs of ice which float up into the Arctic Circle. The bears roam the ice, hunting seals. Sometimes they wait by air holes, waiting to drag an unfortunate seal out of the sea by what passes for its neck. Sometimes the bear will catch the seal napping, although this is less usual. Either way, a typical Great White Bear is expected to eat a seal every five to six days during winter.
Before the banquet, the bears roam the edge of the bay waiting for the ice to form. This is when Churchill becomes a mecca for eco-tourists. Depending on how quickly the cold bites, the bear-watching season runs for between five and seven weeks, roughly from the start of October until mid-November.
The weather is a huge variable, and governs how many bears you are likely to see. When I went (the second week of this month) the ice had had plenty of time to form, and most of the alpha male bears had departed in search of seals. The mothers and their young were still waiting to venture onto the ice to avoid male bears, which eat their cubs, and were hunkering down somewhere south of Churchill.
Yet I saw more than 30 bears in three days. Admittedly six of them were spotted raiding the out-of-town garbage skip, much to the guides' chagrin. The tour firms want visitors to view the bears in their natural habitat, and to see the mighty mammals roaming rubbish tips is a sorry spectacle.
Bears caught around the dump are usually sent to 'Polar Bear Jail' for between a week and 30 days (without food) before being taken by helicopter onto the ice. The idea is to stop them becoming dependent on man. Some people on the trip found this sort of tough love hard to take, but it is a policy honed from experience. The guides who run the trips are wildlife experts. Usually they have an environmental background.
Seeing the bears in the wild, roaming the tundra, is an unforgettable experience, even for those like myself, who find even half an hour of David Attenborough a bit challenging. The mammals are not difficult to spot, huge boulders of sun-bleached fur padding across the frozen wilderness so flat it makes Cambridgeshire look rugged.
Most of the day is spent touring the rim of the Hudson Bay in huge, purpose-built four-wheel drive coaches called Tundra Buggies, part tractor, part runway air crash support truck. The buggies have a secure platform at the back, allowing you to breathe the lung-chilling frozen Arctic air.
This is when bear watching is most rewarding. The sight of a giant bear padding towards you, tongue lagging like a huge labrador, raises the hairs on the back of your neck.
The best thing is when the bears stand on their hind legs and peer into the buggies, allowing those inside to come face to face with the globe's biggest land-living carnivore. It is a truly intimate moment, with the silence broken only by the whir of camera shutters and muffled gasps.
Sometimes the bear will stay around for hours, sometimes it will pad off after only a few minutes. If you're lucky it will roll around in the snow or glide across the ice on its stomach, something guaranteed to generate lots of ooohs and aaaahs from the watching contingent and make you think of Coke ads and Christmas cards.
These are the most precious moments, the moments that make you think it was right to shell out nearly £2,500 for a six-day holiday in sub-zero temperatures in a town not renowned for its nightlife.
People used to the sort of luxury safaris that operate in Africa may be disappointed. The days are heavily regimented, alcohol is relatively scarce and the food basic but hearty. Lasagne and chilli seem to be the staple evening meals in the few restaurants, while lunch is soup and a roll.
Breakfasts, bizarrely, were served in the local Chinese restaurant at the ungodly hour of 6:30 am, allowing us plenty of time to get to the tundra for dawn, a magical time. Sometimes, as dawn breaks through the icy air it causes vertical rainbows called sundogs, totem poles of colour above a frozen sea which stretches across the horizon, an effect which makes you think you are traversing another planet.
This sheer vastness of the landscape, the absence of man, the terrifying, elemental icy quiet in a steel trap of a place is almost as humbling as seeing the bears in the wild. It is to see a world you never realised existed, the way it has been for hundreds of thousands of years.
Along the way you'll also see arctic fox, willow ptarmigan (a kind of snow grouse) and snow owls. Take binoculars: the birds are often to be spotted only from afar.
It is the bears that are the undoubted stars, however. People who have seen them in the zoo may think there is little to separate watching the bears in captivity from watching those in the wild. The two are completely different. Seeing a bear outside a zoo represents a perfect moment; there are no screaming kids and jostling crowds, just an imposing, all-enveloping hush. The fact that the bear is free to leave you whenever it wants adds to the preciousness.
The extreme temperatures make it difficult to stay outside the buggies for more than five minutes, no matter how many layers of clothing you are wearing. If you are thinking ski wear will suffice, forget it: you'll perish. The tour operator can arrange for you to rent the sort of clothing which would not look out of place on a moon landing.
A warming stove makes the buggy cosy inside, but be warned: trying to take photographs from the windows can bring disappointing results because the warmth distorts the pictures. It's better to brave the chill out on the back of the buggy.
Many people on the trip are avowed snappers. Others are keen eco-trippers who will try to psych you out by detailing the other 23 wildife holidays they have been on in the last decade.
And if you're someone terrifed by the idea of spending hours on end with sixtysomething marrieds from Florida - 90 per cent of the tourists are American, most of them elderly - the trip may not be ideal. But for those who want to see nature in her element, there can be few more exhilarating holidays.
