Sisu and sauna
Sisu is a concept used to describe a certain feature that is considered by Finns to be typically Finnish. Sisu is what makes a Finn grit his teeth against all odds; continue fighting against an overwhelming enemy; clear the forest with his bare hands; go on to win a race even after falling over. Sisu is "what it takes": guts, determination.
As for the sauna: Finns get really angry if they hear Swedes or some other lot claiming the sauna as their own. For the sauna is something uniquely Finnish; it is like a holy place for them, a shrine. Originally, the sauna was not only a place for washing but also the place where children were born and the sick cared for. There is an old Finnish proverb to the effect that "if sauna, liquor or tar don't help, the disease must be fatal". In fact, the sauna is where you may well come across the Finnish soul.
Modern Finns also need their saunas. Many flats have their own saunas nowadays, although few have a private lake attached... Of course, people do have different ideas about what a real sauna should be like.