Ognyanovo Mineral Springs

Ognyanovo lies on the right bank of the Kanina River in the Rhodope foothills, roughly 540 metres above sea level and about 12 kilometres from Gotse Delchev. Its bicarbonate-sulphate-sodium waters, rich in silica and fluorine, emerge from two clusters of springs — the main group at 35–39.5°C and a smaller 'Gradski Bani' (Town Baths) source at around 41°C — with a strongly alkaline pH between 8.1 and 9.4. Local use dates back generations, formalised through 1930s–1960s sanatorium construction and the village's 1963 designation as a health resort. The surrounding diatomite deposits are geological evidence that the valley was once a freshwater lake bed. Several modern spa hotels, including the castle-styled Valentina Castle built in 2016 on a hill overlooking the springs, now draw on the same source for their pools.