Where: Bendorf, Germany
Start of construction: 14th Century
Conversions: 1757 & 1848-1862
Most important renovation: 20th Century
Accessible: yes, museum
Important fact:
Destroyed in WWII, but rebuilt afterwards.
The castle was originally a 14th century court of the now ruined Sayn Castle, which stands on top of a hill behind the current castle. https://www.sayn.de/en/