One of the finest invention in the Finnish building history is the chimney. It may not be a Finnish invention but sure has had huge effect on the residents of Finland: I remember reading somewhere that the amount of eye infections and blindness were dropped enormously after the chimney started to gain popularity in the houses and the smoke from the ovens was led outside the house. Despite the total extinction of savupirtti, smoke houses, there is one historical remaining still left from the pre-chimney-era: savusauna, smoke sauna - a sauna with stove but without chimney.
Warming up savusauna is a whole day operation, it takes hours. Why? Because you need to keep the door open during the heating process - of course most of the heat runs away from the door. Smoke on the water, that's what you get when you're warming up a savusauna by the lake. But you must not close the door to speed up the heating, or else you'll just end up burning the whole sauna down or killing yourself with carbon monoxide. Something like 4 to 5 hours is enough to warm up the pile of stones on the stove and also the walls and ceiling.
You need to wait until the flames have burnt out from the very last piece of fire wood - only then you can hop in. But it's all worth the effort and waiting: the heat in the savusauna is unbelievably smooth. The smell can be a bit intrusive first and it takes a while until your eyes get used to the darkness and the remaining smoke - but the löyly, heat is like velvet, you cannot achieve it in any other type of sauna. The heat is mild and firm at the same time. You can actually stay much longer in savusauna, compared to the normal sauna. Just relax and lean back.
After bathing in savusauna you'll clearly notice that you have relaxed. And that you've leant back.