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Some people's idea of health involves a trip to the ice. Sky Travel looks at some of the more extreme examples of these 'ice spas'.
Iceland is not the first place you'd expect to find natural spas, but the volcanic origins of the island not only heats vast thermal pools in the ice, but also forces rock salts and minerals into the warm waters.
Iceland's famous Blue Lagoon is the most visited spa. Its waters are naturally heated at 36°C - 39°C year round.
So, you can easily relax in the water wearing only a bikini, while snow flakes fall all around you.
Once your spa is over, you can indulge yourself further with a massage, sauna or beauty treatment.
After that, why not contrast a morning in a thermal spa with an afternoon of snow-mobiling on Iceland's frozen glaciers.
A bit of thrill is good for the soul.
Going to the other extreme, a number of traditions across Scandinavia and Russia involve swimming not in hot water, but in freezing.
In Finland, a sauna is built in a countryside setting, preferably near a lake or the Baltic Sea. Throwing water onto heated rocks creates a room full of steam in these tiny wooden cabins, which opens up the pores and drains out the toxins.
Then, in an utterly incomprehensibile act, the sweaty occupant dashes outside to plunge into a hole in a frozen lake or into ice-cold sea.
They call this the 'Polar Bear Plunge' and swear by its invigorating effects.
In comparison to Russian practices, though, the Scandinavians appear veritable wimps.
Residents around the Volga River, for example, forgo the sauna bit and simply head out onto the frozen river in the dead of winter.
Armed only with swimming trunks, a towel and a heavy implement, they'll smash a hole in the ice and dive right in. If that doesn't get the heart pumping we don't know what will.

Diving into frozen lakes is also a popular way for some Russians to invigorate the circulation after the excesses of Christmas.
The exact effect is something Sky News' Moscow Correspondent, Alex Rossi, wanted to discover for himself when he followed in the frozen footsteps of these brave souls.
You can watch a video of that on the Sky News website.