What is the right verb to describe a kind of activity which includes rinsing oneself with cold water and/or swimming in very cold water in winter when the air temperature is below zero. What do such people do? Do they harden themselves or what?
In New York City there is the famous "polar bear club", and I have seen a few other groups that do it in news articles. But for them it is a once-a-year event, which they do as a tradition. They don't do it every week or every day.
I have read that some Scandinavians make this a normal part of their "sauna" experience. They leave the very-hot sauna and dip in freezing water, than return to the sauna. But I don't know any American, UK or Canadian tradition like this.