What is "duvalo"

Duvalo is an active geothermal surface feature situated close to the village of Kosel, near Lake Ohrid in southwest Republic of Macedonia. Located at 740 metres above sea level, it resembles a miniature crater with a diameter of 50 centimetres and depth of 30 cm. Gaseous carbon dioxide and sulfur dioxide are released from the hole, and the smell of sulfur is said to be felt in a 3 kilometre radius around it. It represents the last traces of historically significant volcanic activity in the area. During the Ottoman Empire it was used to mine sulfur.