Koshnitsa Kaleto Fortress stands on a dramatic conical limestone peak in the southern Rhodope Mountains near Smolyan, Bulgaria. Dating from the Chalcolithic era (5th-4th millennium BC), the fortress saw active use during the Late Antiquity and Byzantine periods, and again during the Second Bulgarian Empire (11th-13th centuries). Archaeological excavations have revealed a Thracian rock sanctuary from the 5th century BC within the site. The fortress features distinctive double-sided masonry walls constructed with crushed limestone and white mortar, offering visitors a tangible connection to millennia of occupation and defense in this mountainous region.