Frozen exhalation eyelash crystals. It's trending, but you saw it here first.

Frozen exhalation eyelash crystals. It’s trending, but you saw it here first.

Minus 21C doesn’t always look very cold. In photos, at least. But believe me, it is! We discovered this on what turned out to be Beijing’s coldest day in three decades. With wind chill, it was probably closer to -25C, maybe lower still, but -21C was certainly cold enough.

At that temperature, there’s no margin for error. Dressed well, and moving, you can keep your body temperature quite comfortable. But stop, or expose your hands for more than a minute, and you lose sensation in your fingers frighteningly fast. Sitting or even just standing around, you soon feel the warmth depleting. So if you fall and hurt your leg, say, you’re going to have bigger problems than that, really fast. Devices fail in that cold, too, as batteries and LCD screens die. Lucky we knew the way, because the GPS was cactus after less than an hour.

All in all, below about minus 15, I think it’s better to stay home and drink coffee!

Click through for more photos.

Outside temp -21C  (-6F). With windchill, I think it was closer to -25C or below.

Outside temp -21C (-6F). With windchill, I think it was closer to -25C or below.

This all-but-forgotten pass is at Dajiaoyu, on the Beijing Hebei border.

This all-but-forgotten pass is at Dajiaoyu, on the Beijing Hebei border.

A beautiful stand of trees at the base of the pass.

A beautiful stand of trees at the base of the pass.

With my intrepid hiking partner, Ben.

With my intrepid hiking partner, Ben.

There must have been a beautiful watergate at this pass in Ming times, but it's long since demolished.

There must have been a beautiful watergate at this pass in Ming times, but it’s long since demolished.

In my inside pocket, the phone developed some condensation, which also froze. By then, of course, it had long since stopped working.

In my inside pocket, the phone developed some condensation, which also froze. By then, of course, it had long since stopped working.

We couldn't visit our other planned destination because the roads were iced over.

We couldn’t visit our other planned destination because the roads were iced over.

We climbed the wall in the distance first, then sought a route up this snowed-in valley before deciding it was too cold.

We climbed the wall in the distance first, then sought a route up this snowed-in valley before deciding it was too cold.

Ben's dog Dotty handled herself very well too.

Ben’s dog Dotty handled herself very well too.

Everything looked beautiful in the crisp, clear air.

Everything looked beautiful in the crisp, clear air.

When I got home, I found this in my kitchen...

When I got home, I found this in my kitchen…