Sauna
Modern saunas

The sauna known in the western world today originates from Northern Europe. In Finland, there are built-in saunas in almost every house, including communal saunas in the older apartment buildings; since the 80s, private saunas have often been built into the bathrooms of typical Finnish flats in apartment buildings, sometimes even in student housing. There are also a number of public saunas in Finland, including Rajaportin Sauna, a sauna located in Tampere, that was first established in 1906 by Hermanni and Maria Lahtinen. Helsinki even has a sauna built into one of the gondolas of a ferris wheel, SkyWheel Helsinki. Unlike many other countries, Finnish people usually prefer to be naked instead of wearing a swimsuit, towel, or other kind of clothing.

Under many circumstances, temperatures approaching and exceeding 100 °C (212 °F) would be completely intolerable and possibly fatal to a person exposed to them for long periods of time. Saunas overcome this problem by controlling the humidity. The hottest Finnish saunas have relatively low humidity levels in which steam is generated by pouring water on the hot stones. This allows air temperatures that could evaporate water to be tolerated and even enjoyed for longer periods of time. Steam baths, such as the hammam, where the humidity approaches 100%, will be set to a much lower temperature of around 50 °C (122 °F) to compensate. The "wet heat" would cause scalding if the temperature were set much higher.

In a typical Finnish sauna, the temperature of the air, the room and the benches are above the dew point even when water is thrown on the hot stones and vaporized. Thus, they remain dry. In contrast, the sauna bathers are at about 60–80 °C (140–176 °F), which is below the dew point, so that water is condensed on the bathers' skin. This process releases heat and makes the steam feel hot.

Finer control over the perceived temperature can be achieved by choosing a higher-level bench for those wishing for a hotter experience, or a lower-level bench for a more moderate temperature. A good sauna has a relatively small temperature gradient between the various seating levels. Doors need to be kept closed and used quickly to maintain the temperature and to keep the steam inside.

Some North American, Western European, Japanese, Russian, and South African public sport center and gyms include sauna facilities. They may also be present at public and private swimming pools. As an additional facility, a sauna may have one or more jacuzzi. In some spa centers, there are the so-called special "snow rooms," also known as cold saunas or cryotherapy. Operating at a temperature of −110 °C (−166 °F), the user is in the sauna for a period of only about 3 minutes.

According to the Guinness Book of World Records, the world's largest sauna is the Koi Sauna in the Thermen & Badewelt Sinsheim, Germany. It measures 166 square meters, holds 150 people and sports a koi aquarium. The title may now belong to Cape East Spa in Haparanda, Sweden, which also holds 150 people but is more spacious.However, in Czeladz, south Poland, there is now a sauna for 300 people, sporting light shows, theatre and needing several sauna masters.
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