The second day of the three days I spent in Belgrade I visited the Kalemegdan fortress, which is 2000 years old. For many of them the population is concentrated inside the wall. It's a huge space that includes a Housing footprint of the Austro-Hungarian Empire, the Orthodox Church Ruzica (it's visited a lot by college kids before their exams), the Observatory and Planetarium, the Museum of the Navy, a sports area ( tennis courts, basketball, etc.), the Military Museum, The Forestry and Hunting Museum, the Monument of gratitude to France. All of which make it a favorite of locals and visitors, as well as a park with rides with geometric bizarre banks, and picturesque fountains and sculptures that review the history of the country.