The standard type of sauna which has remained unchanged through centuries is the rectangular one room log hut that houses an open rock stove and a raised platform. This is the original savusauna (smoke sauna), which many Finns still consider unsurpassed.
When the rocks in the stove are heated, the smoke from the burning wood circles in the room before escaping through a vent in the ceiling or through the door left ajar during the heating of the sauna. The smoke blackens the room with soot (the floor and the sitting platform are washed before bathing begins) and leaves a pleasant aroma in the sauna. Note that the soot is not dirt but quite contrarily a form of charcoal and has the effect of resisting bacteria.