Rtanj Mountain belongs to the Carpathian mountains and its highest peak is Šiljak (1,565 m), a natural phenomenon of karst terrain. It's a beautiful mountain with a distinct peak, which makes it quite unique. There is a small chapel on the very top of it and you can tell it's there from wherever you look. A lot of mysterious tales are told about Rtanj, local people will tell you about red balls flashing in the night, supposedly aliens visiting the mountain, which is, according to some, full of tunnels and serves as some kind of an alien base on Earth. Rtanj is 17km far away from Sokobanja, and 10km from Boljevac town in East Serbia