Sidirokastro is a city and a former municipality in the regional unit of Serres, Greece. Since the local government reform in 2011, it is part of the municipality of Sintiki, which is the headquarters and a municipal unit. The city is built near the fertile valley of the Strymonas River, on the banks of the Krousovitis River.

There are several UNESCO World Heritage sites nearby. The closest heritage site is the Pirin National Park in Bulgaria, at a distance of 57 km. The closest in Greece are the Paleochristian and Byzantine monuments in Thessaloniki, 57 km north.

Other sights:
- Fort Roupel - is a fortress on the northern border of Central Macedonia, Greece, built in 1914. It became part of the fortifications of the Metaxas Line in the 1930s and became famous for its defense during the German invasion of Greece in April 1941. The fort became famous during the First World War, when the advance of the German and Bulgarian armies was stopped in front of this fort.
- The church in Sidirokastro
- Crama Melidou
- Sidirokastro thermal baths - they are located only 7 km away from Sidirokastro city and operate from the Byzantine and Ottoman periods.