Burg Hardegg

Where: Hardegg, Austria

Start of construction: around 1145

Accessible: yes, interior only with guide

Important fact:

The castle was abandoned mid-17th century and slowly become ruinous. It was partially rebuilt at the end of the 19th century. Private property, but open to the public.
Located on the border of the Czech Republic.

https://www.burghardegg.at/