Located in north China's Inner Mongolia Autonomous Region, Arxan City becomes a world of ice and snow in winter, when the temperature drops to lower than minus 30 degrees Celsius.

Most of the rivers in the region become frozen, except the 20-kilometer stretch in the upstream of the Khalkhyn Gol River. People call this section the "Unfrozen River."

The Khalkhyn Gol River originates from the western slope of the Greater Khingan Range in northeastern China. It's 400 kilometers long.

The ice-free secret lies deep beneath. As it is connected with several volcanic barrier lakes, the upstream section passes over an area of geothermal activity near Arxan. Sitting there is one of the biggest active volcanic clusters in China.

The heat from below allows the river water to stay above the freezing point. Therefore it doesn't freeze like the downstream. And what is more, it even becomes a hot tub for wild animals in the harsh environment in the region.

(Cover is a screenshot from the video.)

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