Petrovaradin Fortress - Novi Sad, Serbia

Petrovaradin Fortress, nicknamed "Gibraltar on/of the Danube" is a fortress in the town of Petrovaradin, itself part of the City of Novi Sad, Serbia. It is located on the right bank of the Danube river. The cornerstone of the present-day southern part of the fortress was laid on 18 October 1692 by Charles Eugène de Croÿ. Petrovaradin Fortress has many tunnels as well as 16 kilometres (9.9 mi) of uncollapsed underground countermine system.
In 1991 Petrovaradin Fortress was added to Spatial Cultural-Historical Units of Great Importance list of the Republic of Serbia.
The minute and hour hands on the clock tower are reversed, with the small hand showing minutes, and the big hand showing hours. It was created as such so that fishermen on the Danube river can see the time from a long distance.
EXIT festival is an annual summer music festival that has been held at the fortress since its inception in 2001. Since then, it has grown from the biggest festival in South-Eastern Europe, to one of the biggest in Europe.