This guide is for the top public saunas in Helsinki. Even though there aren't as many public saunas as there used to be, there are some great ones in Helsinki which fit every price point and levels of authenticity.
Make sure you bring a towel, bathing suit and flip flops. Most Finns do sauna naked, but if a public sauna allows men and women together in the same sauna, then usually you need to wear a bathing suit. Some saunas also include a towel, others do not, but its always handy to have one with you just in case!
Traditionally, you should shower before going into the sauna, then after the heat (5-10 minutes) you should shower in cold water, or go into the sea or cold pool.
This all may seem a bit scary at the beginning, but after you are finished, you will feel relaxed and you will understand why sauna culture is so strong in Finland :)