The Castle can be visited
Museum
Wilhelmshöhe Castle (Kassel)

Wilhelmshöhe Palace in Kassel is internationally renowned for its role as a museum, housing significant art collections. It allows exploration of the authentically preserved rooms of the landgraves.
History+
At the site of the present-day palace, there was originally an Augustinian canonry from the 12th century, which later became an Augustinian nunnery. Landgrave Philipp of Hesse secularized the monastery, and his grandson Moritz had a hunting lodge built between 1606 and 1610, which was expanded in the following decades. The current Neoclassical palace was constructed from 1786 to 1798 under Landgrave Wilhelm IX, based on designs by Simon Louis du Ry and Heinrich Christoph Jussow. During the Napoleonic occupation (1806–1813), it was renamed Napoléonshöhe and served Jérôme Bonaparte as a temporary residence. Later, after the Battle of Sedan, Napoléon III was imprisoned here from 1870 to 1871. From 1891 to 1918, the imperial family regularly used the palace as a summer residence. During World War II, the central section was severely damaged in 1945, and reconstruction began in 1961 in a simplified form, without restoring the original dome.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.3150, 9.4161