Petrovaradin Fortress (Serbian: Петроварадинска тврђава or Petrovaradinska tvrđava, pronounced [pɛtrɔv̞arǎdiːnskaː tv̞ř̩dʑav̞a], Hungarian: Péterváradi vár, German: Peterwardein) is a fortress in Novi Sad, Serbia. It is located in the province of Vojvodina, on the right bank of the Danube river. The cornerstone of the present-day southern part of the fortress was laid on October 18, 1692, by Charles Eugène de Croÿ. Petrovaradin Fortress has many underground tunnels as well (16 km of underground countermine system). In 1991 Petrovaradin Fortress was added to Spatial Cultural-Historical Units of Great Importance list, and it is protected by the Republic of Serbia. Source: wikipedia