After 25 years of war between Sweden and Russia, the year of 1595 finds both countries busy with redrawing their borders. In the 16th century, the drawing of borders was a physical act, a work of practical cartography as well as taxation.
The Finnish brothers Erik (Ville Virtanen) and Knut (Tommi Eronen) Spore are the Southern agents of the Swedish crown deciding on the exact course of the border between the Swedish territory of Finland and Russia. Shortly before they are supposed to meet their Russian counterparts to coordinate and finalize their efforts, the brothers get themselves into trouble in a small village. Erik, a soldier with the charming (and not serial killer-like at all, oh, no) habit of counting the people he has killed (it's getting up to 73 now) slaughters a farmer (let's call him number 74) for the sin of hiding some of his taxable property from him, while Knut, a scientist by trade, very nearly rapes the same farmer's daughter. Unlike Erik, Knut is very much afraid of what he is capable of, stops himself and locks the girl in a cellar, to keep her safely away from harm as well as to not to have to deal with his own emotions. In a moment to delight every hobby Freudian, Knut asks his brother (who is still quite bloody from murdering someone) to free the girl from the cellar. Erik promises to take care of it, and of course doesn't.
Some time later they meet up with their Russian counterparts led by a certain Semenski (Viktor Klimenko), a man who is mostly interested in getting the whole border business over with and finally be able to live in peace. They are nearly through with the work. Just one more pesky swamp and the thing will be over. Semenski is willing to just say that the border is running right through the middle of the swamp without doing any real cartography or putting any markers down in it, but Erik, still fighting the war, insists on real exploration.
Unfortunately for the men, there is in fact something of interest in the swamp, something people as guilt-ridden and morally troubled as Erik and Knut, who has started to see the apparition of a certain dead girl even before, should better stay away from.
It's not the village of war refugees the men find that will be at the core of their troubles, it's an ancient sauna built a little further off in the swamp. But instead of cleansing sins, this sauna was built (if it was in fact built) to make one see one's sins more clearly, in preparation the other things it also shows.
Sauna is one of those films that seem to get better the more crappy contemporary shot on video horror you have seen, but I am not completely sure that it really is as good as It felt like. It is possible, even probable, that the siren song of a film that was not written by a bunch of morons and filmed utilizing mobile phones as cameras with the "director"'s family doing the "acting" is so strong that it makes me overlook certain weaknesses more than I should.
So, let's start with the weaknesses, which can mostly be found in the script. If you take away the historical setting, this is close to a lot of horror films from the last couple of decades, mostly those supernatural horror films which took something different from the Asian horror wave than the jump cuts, but it is at least a film about adults with emotional baggage instead of another film featuring our old friends Final Girl, Slut, Funny Black Guy and so on. Still, deeply original this is not, even less so when you take the bluntness of the film's psychology and metaphors (a girl locked away in a cellar, huh?) into account. On the other hand, Sauna's characters do at least have a psychology.
Then there's a underdeveloped sub-plot about gay attraction in it that is problematic in the way it couples homosexuality and violence, as well as a very unsubtle way to get rid of some characters.
Nearly as ill-advised is the final bunch of special effects. Those might have looked very good on paper, but just don't work in their execution. I am less than sure about their necessity either - for me, the film would be stronger without showing what it shows.
These are all flaws I am willing to live with, though, because these are all flaws that only come into play through the things the film does right. The psychology seems sometimes too reductionist because the acting is good enough to let you believe in the characters as persons; the special effects are problematic because the film is so excellent at setting an initial mood through light and landscape without showing much of anything; the answers are too blunt because the questions are so interesting.
I think the point I am trying to make through my rambling is that Sauna is an excellent film that has the type of flaws a lesser movie won't have because the lesser movie will have failed before it will even have reached the point where these flaws can come into play.