Museum
The Castle can be visited
Greinburg Castle

Greinburg Castle, a prominent historical structure, is situated above the town of Grein in the Strudengau region of Upper Austria. It is considered the oldest residential castle in Austria and exemplifies the transition from a fortress to a castle north of the Alps.
History+
The origins of Greinburg date back to 1488, when Emperor Frederick III authorized the brothers Heinrich and Siegmund Prüschenk to build a castle. This initially served to secure the Machland region. After acquiring the County of Hardegg, the brothers called themselves Counts of Hardegg. Initially known as Stettenfels and later as Heinrichsburg, the current name Greinburg was established from 1533. Under Count Meggau, the castle underwent a Renaissance-style transformation.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:GreinBurg.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 48.2264, 14.8531