It is mid-afternoon but it feels like the dead of night. I've started marathons in the dark before, but usually (as will be the case at next Sunday's Hong Kong event) dawn is never far off. In Tromso, the sun will not rise.
Taking place on the first weekend of each year, the Polar Night Half Marathon is characterised by the beauty, the cold and, of course, the dark of northern Norway. Compared with other marathons, it is as different as, well, night and day.
That's not to say Tromso, with a population of 72,000 and located 400km north of the Arctic Circle, mostly on the island of Tromsoya, experiences 24 hours of pure darkness at this time of year. From about 8am to 2pm, twilight shows off the snow-capped mainland mountains that overlook the city, but by midday a bright moon is already rising.
Heatstroke is no concern for runners of this half-marathon. As pre-race temperatures hover around freezing - quite balmy for this time of year - some runners try to warm up to the techno beats pumping close to the start line; others stomp their feet and jump up and down.
When the horn finally blares, at 3pm, we surge past the brightly painted wooden houses of Storgata, Tromso's main street, under heart-shaped lanterns strung over the road and by the imposing cathedral. Flaming torches planted in the snow alongside the route help light the way, although the glow of the street lamps makes them more of a cosmetic touch than a necessity.
After just a few kilometres we have left the residential areas of Tromso behind and the first flecks of snow begin to fall. Runners head out alongside the main road towards the airport, a black expanse of sea to our left, the darkness broken in the distance by lights shining on Kvaloya, a large island to the west of Tromsoya.
Local residents brave the cold in clusters, to offer support, and every so often some woods provide cover for overhydrated runners needing to make a pit stop.
Although the snow is deep on the edges of the route, the tarmac paths have only a thin coating. Black ice lurks beneath but the spikes that most runners are sporting ensure we stay on our feet.
As we approach the halfway point, the airport (the only real landmark along the route), the lights of Kvaloya disappear as the snow flurry becomes a blizzard. I fear my face is being frozen into a permanent grimace as I exchange sympathetic nods of encouragement with fellow runners.
The snow melting into my many layers of clothing - no doubt combined with too much turkey at Christmas - saps my energy. A sign informs us there are 5km to go, a daunting prospect given the rising layer of snow on the ground. But stopping, or even walking, in the freezing temperatures while wearing sodden clothes is too bleak an alternative to even consider.
Finally, with the snow easing off slightly, we turn back onto the main street, the finish line just about in sight, flanked by spectators on either side of the road. Their cheers warm cold and weary bodies, but not as much as the campfires set up shortly after the finish line do.
Although the snow has given the race an Arctic flavour, it has also obscured the Northern Lights. The half-marathon draws tourists to Tromso - about 60 per cent of the 400 runners last year were from abroad - but the area's main attraction remains the unpredictable aurora borealis. It is possible to see the light show in the city, but for the full effect it's best to venture into the wild.
THE NIGHT BEFORE the run, my friend and I take a crash course in dog-sledding. The five husky cross-breeds that pull the two-person - one sitting on the sled, the other standing at the back trying to brake and steer - carriages can be unforgiving creatures: if you fall off, they won't wait for you to get back on.
We hurtle at speeds of up to 30km/h across snow-covered plains amid the rolling hills on Kvaloya, through forests and across slushy streams. A couple of times I have to duck to avoid hitting a branch while my friend steps off the sled once, only to find herself knee-deep in snow.
About halfway through the 90-minute ride, the sled hurtling along in front of us topples over, halting the six-team convoy.
It is at this point the celestial show begins. A light green smudge in the sky emerges, growing brighter as it swirls and changes shape. It is an experience that seems to demand clichés. Jaws drop. Awe is inspired. And yes, breath is taken away.
It also proves a dramatic backdrop for one couple from Hong Kong to get engaged. If the woman, sitting down, is swept away by the gesture, it is nothing compared with what the man has to undergo, as he suddenly finds himself being dragged along behind his sled, the dogs having decided it is time to speed away. Clinging to the ring in one hand, the new fiance eventually manages to put his weight on the brake, the dogs looking back mischievously to see what all the fuss is about.
LOOKING FOR A slightly calmer way to seek the Northern Lights on our last day, we take a cable car the 421 metres to the top of Mount Storsteinen, on the mainland. From that vantage point, Tromso lies sprawled out, an island of glittering lights in a sea of darkness. Connecting Tromsoya to the mainland is the 1,036-metre-long Tromso Bridge, and at the foot of the hill lies the Arctic Cathedral, a modern pyramid that overlooks a harbour dotted with fishing boats and cruise ships.
Above the inhospitable expanse of snow atop the mountain, the aurora borealis performs a ballet just behind some wisps of cloud.
However, with temperatures falling to minus 6 degrees Celsius, a stiff wind whipping snow into our faces and fingers so frozen they are barely able to hold our cameras, we dive into the warmth of the mountaintop's cafe, to admire the view with a reindeer burger and hot coffee.
Speaking of local fare, Emma's Drommekjokken (or "dream kitchen") is the most acclaimed place in town, the highlight for many customers being a five-course tasting menu that focuses on such regional produce as dried cod and fillet of reindeer. Fiskekompaniet, meanwhile, is an upmarket restaurant serving delicacies brought in by local fishermen and offers a superb view of the harbour in which they land.
Indeed, the city's culinary choices add weight to Tromso's rather far-fetched title of Paris of the North. That sobriquet may be a stretch but, although it doesn't have an iconic tower, this city of light can at least treat you to the natural kind.
Getting there: Finnair flies daily from Hong Kong to Helsinki and operates three flights a week from the Finnish capital to Tromso.