Karst spring. Flow rate 0 - 100 l./sec.
Photos Borislav Borislavov
Note: It is located in the Central Balkan National Park, "Sokolna" reserve, i.e. access is restricted. Its location is outside the marked trails and a permit is required. If you do not have one, you are subject to a fine! Visiting it is at your own risk and keep it clean!