The castle complex with its three wings was built 1695-1720 as the residence of the Protestant princes of Nassau-Siegen.

The Lower Castle is part of the City Tour

Johann Moritz, Prince of Nassau- Siegen, designed the first drafts of the castle layout. His mortal remains and those of his family members were laid to rest in the royal tomb which can be found in the central section of the castle complex. Following the Congress of Vienna, the Lower Castle lost its function as a royal residence and served henceforth as the provincial seat of authority. Following modification work in 2013, the building will be used by both the Faculty of Economics of the University of Siegen as well as the South Westphalian Academy of Small- and Medium-Sized Companies.