Japan may be the only country in the world that still practice this specific training, focused in spiritual strength: the Kangeiko.
寒 Kan = cold
稽古 Keiko = Training
This training goes back to the end of the Edo period, 200 years ago, when in a time of peace, the Spirit of the Samurai warrior was no longer what it once was.
In order to maintain this Spirit some measures to strengthen it and elevate it were taken, and the Kangeiko was one of them.
The Kangeiko occurred on the coldest days of winter, so that the Samurai had to practice furiously and with resilience, and thus overcoming their limits, surviving the times of peace with dignity.
To this end, the Niten annually performs the Kangeiko.