If you ask somebody in Toronto for directions and they say 'it's at the end of the street', you had better make sure you're not standing on Yonge Street at the time. Because 'the end of the street' is a mind-blowing 1178 miles away. Yonge Street is, in fact, the longest street in the world.

Even for Canadians used to titanic distances, the concept of living on the same street as someone a quarter of a continent and time zone away is a bit hard to swallow.

Office worker Lauri looks confused when I stop her to ask directions. "The other end of Yonge Street?" she repeats, staring north. "It's somewhere up there - right?"

Technically yes. But we're standing in downtown Toronto where Yonge Street begins, and it doesn't, as Lauri assumes, end on the outskirts of the city. In fact, Yonge Street roars through Toronto and then straight through the Ontario wilderness right into the sub-Arctic, across the top of the Great Lakes. The street ends only when it smacks straight into the U.S. border at Rainy River, Minnesota.

I reckon the trip will take four days, but the seasons are changing and I need a car that's up to potentially rotten weather. So I've opted for a Mercedes-Benz E-Class for what promises to be an unpredictable journey. Our E-Class packs the company's sensational, 387-hp V-8 and a clever four-wheel drive system that should keep us well out of trouble when the snows come. The Merc's also got a host of safety equipment that will keep us between the ditches.

"It's not a bad choice," reckons policeman Mal Chivers. "Snow, leaves, ice, animals, drowsy drivers -- you'll run the gamut this time of year. We patrol the whole of Yonge Street. It's a monster."

Before leaving the city, we take in the Hudson's Bay Company, which is arguably the single most important entity in Canadian history. It was mainly Scottish fur traders and pioneers established remote outposts and claims to the vast Canadian bush that kept Britain's hold on this immense expanse of wilderness.

Across the street I meet Toronto expert Richard Fiennes-Clinton from Muddy York Walking Tours at the Elgin Theatre. The theatre opened when Yonge Street was a thoroughfare for horses and carts.

"The street earned its importance as one of the routes down which the furs and other riches from the north came to market in Toronto. Past here you would have seen the wealth of the country come by," he explains.

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The next day's a long drive, even by Canadian standards. Cochrane to Thunder Bay -- the largest city outside Toronto on Yonge Street -- is just short of 500 miles.

This is where the Merc really comes into its own. With such massive distances to cover, drivers routinely fall asleep at the wheel on Canadian roads - our E-Class has a system that rouses you with a buzzer and a picture of a coffee cup if it senses you getting drowsy. Likewise, if the car begins to wander on the road, the steering wheel vibrates to warn you that you're going off course.

My only planned stop was to be Kapuskasing, a place so cold in winter that car companies test their vehicles there. But I couldn't resist pulling over at the sight of a flying saucer parked by the highway in Moonbeam, Ontario. A sign informed me I had now arrived at the self-styled UFO capital of Canada.

Former car tester Pierette Peters sees me hovering by the saucer and comes over to chat. "I was out on Yonge Street one night when I saw glowing lights hovering in the night sky," she recalls. "I have seen them, others in Moonbeam have seen them. Nobody can explain it. But whatever anybody else believes, I'm convinced UFO's exist."

Waking up for my last push towards the end of Yonge Street, a dusting of snow has fallen and the time zone has changed. Up here the skies and unbroken horizons are so huge I can sense the globe curving.

The Merc has clocked up the miles without complaint, providing a quiet and refined platform from which to view this remarkable road.

And finally we're there -- Rainy River marks the spot where Yonge Street finishes. A lonely road sign reads, simply, "ENDS," and standing there, Toronto is but a distant memory.