Where: Potsdam, Germany
Constructed: 1835-1849
Most important renovation: 21st Century
Accessible: no, because of renovation works.
The surrounding park is accessible though.
Important fact:
built by order of then prince Wilhelm I.
The future German emperor used the castle
as a summer residence for 50 years.
https://www.spsg.de/en/palaces-gardens/object/babelsberg-palace/