If you're the type to enjoy a good sweat, then consider a Korean kiln sauna. The kiln sauna, also known as the han jeung mak, is a Korean tradition dating back to the 15th century. Burning pine tree wood sets the stage inside a stone structure with a low opening. Users are given jute blankets to protect themselves from the intense heat. How hot is the kiln? According to the New York Times, temperatures can reach nearly 400 degrees F. If you wore synthetic clothing in there, it would melt. Lim Hyun-o, who works at a kiln sauna in South Korea, told Times, "Some arthritis and cancer patients rent rooms around here and patronize the kilns for months. We believe that the heat in the kilns sweats the toxins out of our bodies."