The Castle can be visited
Museum
Belvedere Castle

The pleasure palace complex Belvedere Palace in Weimar is distinguished by its Baroque architecture and extensive landscape park. As part of the “Classical Weimar” ensemble, it has been a UNESCO World Heritage site since 1998.
History+
The construction of Belvedere Palace took place between 1724 and 1744 under the direction of master builders Johann Adolph Richter and Gottfried Heinrich Krohne. It served Duke Ernst August I of Saxe-Weimar as a residence and was one of about twenty of his hunting and pleasure palaces, with the Vienna Belvedere Palace serving as inspiration. From 1806 to 1853/59, the Weimar princely house, particularly Hereditary Grand Duke Carl Friedrich and his consort Maria Pawlowna, used the palace as a summer residence. After 1921, ownership transferred to the state of Thuringia.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=586
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: 50.9483, 11.3491