Where: Larochette, Luxembourg

Start of construction: 12th Century

Accessible: yes

Important fact:

In 1565 hit by a large fire.

after which the castle slowly became ruinous.
Bought in 1979 by the Luxembourg state, which had one building (Chriechinger Haus) restored.
The rest of the complex is still in ruins.

https://www.visitlarochette.lu/en/discover/castles-and-fortifications