Actually, the yoga bit is the brainchild of 28-year-old Rebecca Bjork, and on paper it sounded so enticingly healthy and outdoorsy — lots of exercise, a bit of meditation, then snowshoeing yomps through Christmas-card forests. In reality? Well, despite three pairs of socks and thick boots, my toes feel on fire and I am not sure whether I still possess a nose. And when Rebecca urges us into a sun salutation, I cannot help but giggle. Sun? It’s night-time! And besides, winters here barely register daylight let alone the sun.

And then the magic begins, and by the time we have muttered “namaste” I am feeling better. Remarkably clear-headed, in fact. And that is because I have started to follow instructions, allowing my body to adapt slowly to the chill and our gorgeous surroundings.

Warm up: the sauna at the Aurora Safari Camp

There is the bonus of an endorphin rush from working hard to stay warm, and soon I focus less on my aches and more on the heartbeat sounds of water rippling beneath the ice. Above us, the Plough is pinpricking a velvety sky, while behind Jupiter shines with torch-beam ferocity.

Let me scroll back in our journey, though, to this, the Aurora Safari Camp. Swedish Lapland is seriously remote and is bigger than Austria, but with a population of less than 100,000. Dour Scandi-noir warnings from our driver accompany our trip along snow-banked roads flanked by forests of fir and spruce. “You always have to think about fuel,” he says. “Have you got enough? Get stuck and there’s no convenient garage or house near by. You could easily die in these temperatures.”

Well at least the bears are in hibernation, we think, as the road switches to a side turning that swishes towards our camp. There is a lodge at the entrance, stuffed with Michelin Man-style snow overalls and grip boots. Hats and gloves too, and once we have puffed our way outside, we have a fur-draped bench waiting, pulled by a snowmobile. Think of a Santa snow carriage, updated.

Off we whizz over the frozen Degerselet Lake, icy wind whipping our cheeks, our gazes held by the diamond dazzle of snow captured in the lights.

The camp is gorgeous. It is an hour north of the city of Lulea and an hour south of the Arctic Circle. And there is no light pollution — hence the stars, and for those lucky enough a good chance of aurora sightings.

Our home is a traditional Sami Lavvu tent, with proper beds and a wood-burning stove that Pietri, one of the team, refuels hourly throughout the night. It is all very hygge, with thick duvets and rugs, but I am fretting about finding the loo in the dark and deep snow. I will gloss over our short-cut decision and instead focus on how this weekend unfolds.

Mornings usher in breakfasts of cement-thick porridge followed by hatha-style yoga on furry reindeer mats, with evening sessions to close. Yoga bunnies might find the elementary level of these and the cumbersome snowsuits frustrating, but as Rebecca insists: “This is as much to do with the environment as the yoga. Breathing this fresh air will give you immense energy.” So I do breathe in, enjoying the crisp, nose-freezing air, watching as the late-rising sun pricks the horizon with a crimson glow and highlights trees thick with unfathomably convoluted icicles.

After breakfasts of cement-thick porridge comes a morning of hatha-style yoga on furry reindeer mats

Afternoons are taken over by Peter Lundstrom, from Swenature, which means a fabulous snowshoe shuffle through the Bjuroklubb Nature Reserve. This is the most eastern tip of Sweden fronting the frozen Baltic Sea — a barren place so cold that our phones are leached of battery life — but maybe that is the point of a retreat. It certainly helps to focus our attention on how uncannily pink the iced-over Baltic appears set against a metallic blue sky.

As we walk, Peter guides us in the Morse code of animal tracks, pointing out the dot-dot-dash of an Arctic fox, the half-crescent grooves of deer and smaller indentations from hares. It is the sounds that really entrance though, our ears attuning to the soft whistle of wind through the trees and the scrunch of virgin snow beneath our feet.

Later, against a backdrop hiss from the sea beneath thick ice, Peter rustles up an alfresco lunch consisting of strips of reindeer, potatoes and onions, cooked on a small fire over the snow. It is delicious but filling, for food in this part of Sweden is necessarily calorific.

Not that what we eat always appeals. Later that evening, as we sit outside, a huge, golden moon glowing low on the horizon and the temperature hitting minus 17, Rebecca cooks up palt — potato and flour balls fried in butter and doused in treacle and lingonberry jam. There is milk to drink, with shards of ice floating on its surface.

One of us mutters how she would kill for a G&T but these thoughts are cast aside by the smell of our next course — surstromming — a long-fermented herring so pungently drain-like that it has us gagging for air. Outdoors. “Yes, it’s an acquired taste,” Rebecca says with a laugh as I take a bite then promptly spit it on to the snow.

It manages to take my mind off the cold, as does the tented sauna where we huddle later, enjoying the welcoming warmth. Not for long, though. There is a hole bored into the icy lake. “Just take a dip and slowly recite your name — you won’t feel the cold,” says Rebecca. And oddly, she is right. Dressed in a bikini I pluck up courage and lower myself to waist level.

After that, a snowsuit seems positively overkill.

Need to know
Louise Roddon was a guest of Active North (activenorth.se), which runs yoga retreats at three Swedish Lapland locations. A four-day/three-night retreat costs from 12,500 krona per person (£1,135), including full board, activities and transfers. Return flights to Lulea via Stockholm with Norwegian (norwegian.com) are from £160. For further information visit swedishlapland.com