Pernik is a city in western Bulgaria (about south-west of Sofia) with a population of 80,191 . Pernik is the most populated city in western Bulgaria after Sofia. It is the main city of Pernik Province and lies on both banks of the Struma River in the Pernik Valley between the Golo Bardo Mountain, Vitosha Mountain, Lyulin and Viskyar mountains. Pernik is the main city of Pernik Province - province in western Bulgaria, neighbouring Serbia.