Unteres Schloss, Castle in Siegen, Germany.

Unteres Schloss is a large castle complex in the heart of Siegen, made up of several wings built across different periods. The complex includes residential and administrative buildings as well as a castle church, all arranged around a central courtyard.

A Franciscan monastery stood on this site from 1489 until 1534, when Count Wilhelm expelled the friars. From 1668 Johann Moritz of Nassau-Siegen converted the former convent into a residence, adding a princely crypt and a gallery wing. His successor Wilhelm Moritz began a new building in 1680, and the gatehouse followed in 1690.

The princely crypt, the Fürstengruft, was created around 1668 by the Dutch builder Maurits Post inside the former monastery building. Johann Moritz von Nassau-Siegen, who commissioned it, was only transferred there from Kleve in 1680. His nephew Wilhelm Moritz later added a connecting wing to the crypt.

The complex sits in the center of Siegen and is easy to reach on foot. Because it is made up of several wings, it is worth setting aside some extra time to explore the different areas without rushing.

The Siegerlandmuseum is housed in the Oberes Schloss, not the Unteres Schloss. The Unteres Schloss is instead being developed as a new campus of the University of Siegen. Its former Franciscan church, dedicated to John the Baptist, served as a Protestant town church until 1624 and was destroyed in the 1695 town fire.