Underground military galleries is a four storey communication and defensive system 10 miles long. This complicated system was built in 1783 and it represented a real tourist attraction. Tour guides show web of corridors and rooms, crenels and mining systems. After the Antwerp’s, this fortification has the most effective mine fields. Curiosity of Petrovaradin is that it was never conquered, therefore, during the 19th century, here was the treasure chamber with gold and silver of the Habsburg Empire. The fortress had been built during the reign of the Habsburg dynasty and Habsburg-Lorraine with rulers: Leopold I, Carlo VI, Maria Theresa and Joseph II. Maria Theresa (ruled from1740 to 1780) had never visited Petrovaradin fortress but it is well known that she granted (for the sum of 80000 forints). The Petrovaradin moat the status of the free royal city on February 1st, 1748. From that time on, the town was called Novi Sad, Neoplanta, Újvidék or Neusatz. Her son, Joseph II (ruled from 1780 to 1790) visited Petrovaradin fortress four times.