The remains of the Castle can be visited
Hammerstein Castle

The Hammerstein Castle Ruin, a hilltop castle, stands on an elevation overlooking the Rhine in Rhineland-Palatinate. It is considered to be the oldest castle complex in the entire Middle Rhine Valley and dates back to the 10th century.
History+
The origins of Hammerstein Castle lie in the 10th century, when the Konradiners erected it in the Engersgau. Already in the year 1000, it was mentioned as an imperial castle. A siege took place in 1020, when Emperor Henry II captured the castle because Otto von Hammerstein was in an unrecognized marriage. After its decay, Emperor Henry IV had the castle restored in 1071. In 1105, the imperial insignia were retrieved from here. In 1417, the castle became an imperial fief of the Archbishopric of Trier.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Joachim Schneeleopard
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: 50.4714, 7.3578