The Istibey fortifications are on Mount Belles. It was Fort Istibey and Forts Kel Kagia, Usita, Partaluska, Pallyriones, Popoplivitsa, Arpalukio, Echinos, Rupel, Perithorio, Dasavli and Lisse that for two days, the 6^th and 7^th April 1941, held back the attack against Greece by German and Bulgarian forces. In 1991 the Panhellenic Association of Combatants and Friends of the Forts of Macedonia and Thrace funded the construction of a small museum on this site to remind younger generations of the heroic resistance Greek forces offered against the forces of the Axis.

Getting to the museum is no mean feat. First of all permission must be obtained from the military unit stationed at Petritsi, which is four kilometres off the Serres-Promahona National road (Kilkis junction), then the steep fourteen-kilometre-long road leading to Fort Istibey must be negotiated. Foreign nationals must have obtained a special permit from General Army Headquarters.

The museum contains firearms (rifles, revolvers, pistols and machine-guns) belonging to the Greek and German armies, army uniforms of the time, various personal belongings of the defenders, as well as a map detailing the Battle of the Forts. During visits a film is also shown, which tells the story of the battle at Fort Istibey.