The 25 year long war between Sweden and Russia comes to a close and two brothers, Eerik (Ville Virtanen) and Knut (Tommi Eronen) are on their way home, part of a team that is mapping the new border. On the way they stumble upon a village in the middle of a swamp where their guilt catches up with them.
Aesthetically, Sauna is a visual pleasure: long sweeping takes of desolate marshes recall Gothic horror like that of The Innocents. Though the specter that haunts them is less The Woman in White and more Lavinia from Julia Taymor's Titus - but with vengeful streak. Hallucinations are so subtly shot that we, like the brothers, question what see, whether it's bodies beneath the swamp's surface or a statue oozing black blood. Though this haunting continues to the end, Sauna is not so much about paranormal activity as it is about inner guilt and turmoil. In a scene which mightily disturbs our orthodontic-centric age, Semenski (Viktor Klimenko) begins loosing teeth, followed shorty by his mind. The fear then lies not in what's coming to get them but that it's already there, rotting from their insides.
Much of the movie is also spent hovering at the entrances of dark doorways. In terms of narrative this builds the tension for when Kunt finally enters the sauna (trust, it's no executive workout). But it also works on a thematic level: both brothers are constantly on the edge of stepping into their own personal darkness.
Sauna also has one of the most terrifying endings I've had the (dis)pleasure of watching. Rounded off with a circular narrative and lack of closure that leaves the audience with unanswered questions it's a complete package. As I said before, see it. You'll never look at Finnish spas the same way again.