The German Horticultural Museum is located in Cyriaksburg Castle within the egapark grounds. Construction of the castle complex began after 1480 and two strong round towers are still preserved from this old fortification. During the Thirty Years' War, Cyriaksburg Castle was under Swedish occupation. The famous physicist Otto von Guericke is said to have been involved in reinforcing the fortifications during this time. Most of the parts of the building still visible today date from the period 1825 to 1829, when the Prussians converted the castle into a fortress in the neo-Prussian style. The fortress well, which is around 40 m deep, is located in the underground part.