The Trigrad Gorge (Bulgarian: Триградско ждрело, pronounced [triˈɡratsko ʒdrɛˈɫɔ]) is a canyon of vertical marble rocks in the Rhodope Mountains. It is in Smolyan Province, one of the southernmost provinces of Bulgaria. The gorge encloses the course of the Trigrad River, which plunges into the Devil’s Throat Cave and 530 metres (1,740 ft) further emerges as a large karst spring. It later flows into the River Buynovska.
Source: Wikipedia
