A hopothermic-religious experience
On January 19th the Orthodox Church celebrates the Baptism of Christ known as Theophany, or Epiphany. In accordance with ancient church tradition, Orthodox Christians bless the nearest body of water, be it a river, lake, or pond.
After this blessing, the water is considered to be holy and all the faithful come to dunk three times in the name of the Father, and of the Son, and of the Holy Spirit. The act is meant to symbolize the baptism of Christ.
In Russia, an estimated 33 million come out to do the ice plunge! This year temperatures reached -55 C / -67 F (!) so we've included a clip of today's Russian news coveing it below as well.

Here's 2017's dunk with yours truly and my fearless wife, Liz:
Russian news coverage of -55 C dunks
And here's Russia Insider's 2016 dunk: