Heptabergion Thessaloniki Castle, also known by its Ottoman Turkish name "Yedi Kule", is an ancient Byzantine and Ottoman castle, located in the northeastern corner of the Acropolis of Thessaloniki in Greece. Exploring this abandoned centuries-old castle is like stepping into its past. During its tenure as a notorious prison, its walls witnessed a history tainted by torture and brutal executions. This castle has seven high towers, and has a Byzantine-style building.