Istisu is a hydrogen-sulfide treatment center. The local people call the water a “miracle”. Hot water of 69o C comes from under the ground here, hence the place-name Istisu (hot water). This water is used to treat problems with joints and muscles, skin, gynecological and other diseases. The local sanatorium has mineral water baths as well. The water coming from rocks at Istisu is ice cold. Rich in hydrogen-sulfide, it smells like rotten eggs. It is poured into a glass and drunk in one gulp. There are “kidney water” and “stomach water” signs above the springs. Spring water can heal ulcer and kidney stones. The curative properties of the Istisu water were studied in the 1950s. A Masallli-native geologist Mir Kazim Aslanli even defended a thesis on the subject in 1955. The local treatment center received the status of a sanatorium in 2007. Due to its subtropical climate, the rate of precipitation in Masalli is higher than elsewhere in the region. Frequent rains make the Talysh forests even more romantic. Istisu forests are 12 km from the center. Istisu is beautiful at any time of the year. In autumn, one can see all colors of nature here. There are not many hotels working in this season. To witness the entire beauty of Istisu, it is worth visiting in spring, autumn and winter. There are fewer people and the relatively cool weather makes the local baths very pleasant. Whereas it is difficult to spend more than three to five minutes in the bathtub in the summer, one can swim for hours when the heat is not oppressive. The feeling after an Istisu bath is one of relaxation. If you have wounds or gashes on your body, you can see what wonders the water can work.In the summer the forest looks different as scores of people come here for treatment in July and August.Istisu is also famous for its waterfalls. They make the place even more gorgeous. Hiding deep inside forests, waterfalls make their surroundings a little cooler, which attracts people to picnics.