The remains of the castle can be visited
Herzogenstein Castle

The unfinished remnants of Herzogenstein Castle, also known as Rheineck, are a 14th-century hilltop castle. The site is located on an elevation near Dörscheid in the Rhein-Lahn district of Rhineland-Palatinate.
History+
In 1359, Count Palatine Ruprecht I planned the construction of a hilltop castle on the Roßstein, a rock formation near Dörscheid. This endeavor was intended to secure the Palatinate's possessions on the right bank of the Rhine in the Middle Rhine region, acquired in 1277. However, Archbishop Boemund II of Trier and the city of Oberwesel intervened against the construction, fearing disadvantages for Rhine traffic if the castle were to become a toll station. After an initial agreement, Ruprecht I continued the construction work, which led to armed conflicts.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Frank Winkelmann / CC BY 3.0 via Wikimedia Commons
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: 50.1169, 7.7289