GALLERY Every culture, through every age, has enjoyed its own form of sweat bathing. From the Ottoman hammam and Mayan temazcal to the Japanese mushi-buro and kama-buro, from the banyas of Russia to the saunas of Finland, heat therapy has stood the test of time, waxing and waning in popularity and crossing continents in various iterations. Scientists say regular saunas help lower blood pressure, reduce the risk of cardiovascular disease and dementia, boost immunity and help with fatigue, depression and more. There’s a reason why sauna-loving nations, such as Finland, Sweden and Norway, jostle for the top spots in the annual United Nations World Happiness Report. People feel good after a sauna session and have done for centuries. And now the world is once again waking up to the incredible…