Following a pickup from your hotel, travel directly to Nis in Serbia. Arrive in Nis after a 2-hour drive and explore the town known as the birthplace of the famous Roman Emperor Constantine the Great. Your first stop will be the Skull Tower, also known as Chele Tower. Marvel at the stone structure embedded with human skulls. It was constructed by the Ottomans following the Battle of Cegar of May 1809, during the First Serbian Uprising. The next stop is the former concentration camp, opened in 1941 during World War II. More than 10,000 people are thought to have been killed at the camp. Today, you can explore the museum and learn about its dark history. The final stop leads you to the city museum in Nis where you can find all archeological findings from the area and learn about the long history of the town. After a guided tour of the most important monuments, enjoy 1.5 hours of free time to explore the city. Take a stroll along the central pedestrian street and visit the local shops and restaurants with their delicious food. You’ll return to Sofia at around 6:00 PM.