Not far from Perperikon Perpereshka river flows into Studen Kladenets dam (the name means ‘Cold Well’), built along Arda river bed. The exact place where the river flows into the dam, by Kaloyantsi village, is very beautiful and is built-up as a mountain water resort. Here you will see one of the largest Rhodope fortresses (12 000 sq.m.), situated on Kamennik hill, in the East Rhodopes. The area is known as Gin Tepesi (or the Mountain of Ghosts). The remains of ancient walls are preserved, as well as the 10-metre wall of the hexagonal tower. In the beginning of the century the famous fortress researcher Ivan Velkov discovered the tower well-preserved. He climbed the stairs and watched through the loop-holes. An ancient cistern is also preserved. It is 12m by 5m and 6m deep.