We should note that all of these places of thermal extremes (Finnish saunas, Japanese hot baths, American beaches and mountains) have their opposites close at hand. There are possibly two reasons for having the extremes right next to each other.
The first is physiological: the availability of extremes ensures that we can move from one to the other to maintain a thermal balance.
The second might be termed aesthetic: the experience of each extreme is made more acute by contrast to the other.
Works of art which have great life often have intense contrast within: rough/smooth, solid/void, loud/silent, empty/full. It is the difference between opposites which gives birth to something. Contrast is what often gives other principles their degree of life – the intensity of the boundary, the markedness of the alternating repetition.
Contrast strengthens centers by making each a deeper entity of itself, and thereby giving deeper meaning to both. It is, at its simplest, what allows us to differentiate. But meaningless contrast remains meaningless. It is only when centers are actively, mutually, and meaningfully composed that it acts to deepen the whole.
Years ago a friend of mine had a dream about a strange invention; a staircase you could descend deep underground, in which you heard recordings of all the things anyone had ever said about you, both good and bad. The catch was, you had to pass through all the worst things people had said before you could get to the highest compliments at the very bottom. There is no way I would ever make it more than two and a half steps down such a staircase, but I understand its terrible logic: if we want the rewards of being loved we have to submit to the mortifying ordeal of being known.