PA PHOTOS / DPA – UK USE ONLY : Guests sit and sweat in a traditional Finnish Tuli (fire) sauna in the Puutarha Sauna in Frankfurt Oder, eastern Germany. The advantages for health and well being are well known to science. Digestion, the sweat regulation of the body as well as the immune system are in full cry. It refreshes head and body. The effects have been known for thousands of years but only the Finnish managed to develop a proper sauna culture over 2000 years ago. Today there are around 1.5 million saunas in Finnland for a population of 4.5 million.