The remains of the castle can be visited
Königstein Castle

Known as Ecker G’schlössl, the Königstein castle ruin is a historical structure in Upper Austria. It is situated on a hillside spur above the Kösslbachtal valley in the municipality of Freinberg and has a well-documented short history, as its construction and destruction dates are known.
History+
The construction of Königstein Castle began on Epiphany in 1410, commissioned by Duke Johann of Holland-Straubing. Its purpose was to control trade routes to Passau and possibly to protect against the Hussites. Already in 1411, disputes arose with the Bishop of Passau, which were settled by a truce. After Duke Johann's death and the division of Lower Bavaria, conflicts reignited under the new owner, Ludwig the Bearded.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:K%C3%B6nigstein_Bergfried.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: 48.5594, 13.5414