Banská Štiavnica (Slovak pronunciation: [ˈbanskaː ˈʃciawɲitsa] is a town in central Slovakia, in the middle of an immense caldera created by the collapse of an ancient volcano. For its size, the caldera is known as Štiavnica Mountains. Banská Štiavnica has a population of more than 10,000. It is a completely preserved medieval town. Because of their historical value, the town and its surroundings were proclaimed by the UNESCO to be a World Heritage Site on December 11, 1993.