During the Second World War, Stixenstein Castle, thought to have been built originally in the twelfth century, was one of sixteen depots in Lower Austria for objects from the Wiener Städtische Sammlungen. In 1937 the municipality of Vienna had acquired the Stixenstein source to safeguard the city's water supply. It acquired title to the castle at the same time. Because of its remote location at the end of the narrowing Sierningtal valley on a hill on the road from Sierning to Puchberg, Stixenstein Castle was deemed to be an ideal storage site for artworks salvaged on account of the war. As in other Städtische Sammlungen depots, storage began in August 1943, after the museum had been closed for the duration of the war following an air raid on Wiener Neustadt. Three floors of the castle were filled with a wide variety of objects: furniture, musical instruments, oil paintings, measuring instruments, busts, stained glass windows, porcelain, chests, miniatures, flags, armour, shields and crates with books from the city library. The depot was guarded by members of the city of Vienna forestry department.

There was heavy fighting in the region at the end of the war, and the castle was captured by the Red Army on 2 April 1945. Around 350 Soviet troops were massed to ward off attacks by "Kampfgruppe Keitel". Items from Stixenstein began to be returned from early August 1945. Huge losses were incurred, however, on account of looting by Soviet soldiers and the local population. In addition, the Soviet administration has seized twenty paintings for the officers' mess in Neunkirchen, which were not returned to the museum until the conclusion of the State Treaty in 1955.