Before 1942, the Salzgitter area was divided between the states of Braunschweig and Prussia. Both had different laws and ordinances that hindered the development of the Reichswerke. A municipality had to be found that could act as a "contact partner" and implement the "wishes" of the Reichswerke. Thus, on April 1, 1942, by law of Reichsverteidigungskommissar Jordan, the independent town of Watenstedt-Salzgitter was founded from around 30 villages around the smelter and the mines, the small town of Bad Salzgitter, the barrack camps and the large housing estate begun in 1939 and the smaller settlements.

The history of the town of Salzgitter in the 20th century is summarized in the Salder Castle Municipal Museum on around 500 square metres in the "Horse Stables" exhibition building.

The exhibition begins with the end of the Weimar Republic and everyday life in the villages of the Salzgitter region. After the National Socialists came to power and their efforts to become self-sufficient in foreign raw materials, life in this region changed abruptly.

From the mid-1930s, thousands of workers came to the Salzgitter region to mine the ore and build the steelworks at the same time. Due to the lack of living space, they initially had to be housed in barrack camps. The history of these camps, in which prisoners of war and concentration camp inmates later had to live, and the planning of the Hermann Göring City take up a large part of the exhibition.

At the end of the war, the city was faced with almost unsolvable problems. The steelworks were to be completely dismantled and an infrastructure for the city was to be created on the drawing board. In addition, thousands of refugees and displaced persons were looking for work and housing. Life in the 1950/60s is the focus of another facet of the exhibition.

The exhibition ends in 1989/1990 with the restoration of German unity and a presentation of Salzgitter's twin towns.