Rupel fortress is located between the mountains Aggistro and Belles, very close to the Greek-Bulgarian borders. It is the largest complex of the fortified location situated along the Greek-Bulgarian border, called "Metaxas Line", with the total length of the fortification chain to be 1.849 meters and with 4.251 meters long underground galleries. It is a truly strategic location that perfectly controls the communication in the valley of Strymonas river. The Greek side fortified the area in 1914 with the construction of the fort, well known from both world wars, since it was the battlefield of Greeks against the Germans. Today, open to visitors are a gallery of the fortress, a small museum, the visitors’ pavilion, the observatory and the Monument to the fallen.