This is the Burg Rabenstein castle, which is said not to be well-known in the world and even within Austria itself. I guess thats why maybe there are not many information on the internet, at least not in English. But I came across some person's own experience of this place, so im conveying you his thoughts here...
"...Rabenstein is designated as an international cultural property by the Geneva Convention, and it is consequently protected from harm or use by military forces during times of war. In the 18th-19th century it was privately owned and used as a hotel, but today the small castle is owned by the Austrian Government in a specific capacity unknown. Apparently an official from the nearest town of Frohnleiten (a scant 3 kilometers away) presides over the castle and maintains its appearance. In summer the castle's courtyard is used by a local theatre group to present original dramas by Austrian playwrights.
Rabenstein is in immaculate condition, with magnificent lush flower-gardens and a fishpond in its courtyard, a freshly painted edifice, and a thick old-wood forest surrounding it on the steep hillside. And the Roman ruins, though crumbling and decrepit, still surround the rocky perch and stand majestically over the narrow valley...."
the above paragraph is courtesy of Jason Charles Buss, who I guess had quite a nice experience when visiting this castle.
and a nice birdy stamp (my cats would go frantic with so many birds, even if only on stamps :))
This one shows a Common Kingfisher and was issued in 2008 in a set of two stamps.