Kastel Fortress, also known as Kastel or Kastel Gradište, is a historic fortification located in the city of Banja Luka in Bosnia and Herzegovina. The fortress sits on a hill overlooking the city and the Vrbas River. It has a long and rich history, dating back to Roman times when it was originally built as a military camp. Over the centuries, it was expanded and modified by various ruling powers, including the Ottomans and Austro-Hungarians. During World War II, the fortress was used as a concentration camp by the Nazi-allied Ustaše regime.
Today, the fortress is one of Banja Luka’s most popular tourist attractions and cultural landmarks. It has been renovated and restored several times over the years and is now home to a museum and an art gallery. Visitors can tour the fortress and learn about its history, as well as enjoy stunning views of the city and surrounding landscape. In addition, the fortress is often used as a venue for cultural events, including concerts, theater performances, and art exhibitions.