Golubac Fortress - Credit: Wikimedia Commons
The Golubac Fortress ( or Golubački grad) was a medieval fortified town on the south side of the Danube River, downstream from the modern-day town of Golubac, Serbia. According to recent discoveries, the fortress, which was built during the 14th century by Medieval Serbian state, is split into three compounds which were built in stages. It has ten towers, most of which started square, and several of which received many-sided reinforcements with the advent of firearms. Towers were not connected for easier defense. Serbian Medieval frescos were recently found inside the fortress. Read more on Wikipedia
Source: en.wikipedia.org