First generation: Sauna pits in ground, covered with animal skins (10,000 years ago)

Second generation: Ground sauna: earthen floor, three walls dug into the ground, fourth wooden door wall, and a turf roof piled on a few tree trunks

Third generation: Sauna as an above ground building: smoke sauna, used mainly until 1930 (take a lot of firewood, and heating time)

Fourth generation: Saunas equipped with chimneys: spread in 18th and 19th century city saunas

Fifth generation: efficient saunas built to accommodate the poverty that followed the war: small and continuously heated stove with a light sheet metal shell (fire kept burning DURING bathing) took only 30min to heat

Sixth generation: In home electric sauna: due to no fire or wood, sauna is part of home again. Ready in no time

Seventh generation: intelligent sauna with mechanical ventilation and computer controlled electric stove.

Eighth generation: Mobile sauna (buss, pontoons, skis) etc.

Ninth generation: Cultural sauna, public saunas designed by artists, experimental saunas designed by architects. A return to the sacred.