The remains of the Castle can be visited
Royal Palace Kaiserswerth

The ruin of the Kaiserpfalz Kaiserswerth is located in the Kaiserswerth district of Düsseldorf. Its location on the Rhine makes it a testament to medieval architecture and power politics.
History+
The origins of the Kaiserpfalz date back to the early 8th century, when the Frankish Mayor of the Palace Pippin the Middle and his wife Plektrudis gifted the monk Suitbert an artificially created Rhine island, where a fortified manor already stood. This developed into a customs fortress. In 1016, a castle there was first documented when Emperor Henry II granted it to Count Palatine Ezzo. After Ezzo's childless death in 1047, Kaiserswerth reverted to the Empire, and Henry III had the castle expanded into a palatinate. However, this first Salian complex is no longer preserved today. Kaiserswerth gained notoriety through the royal abduction of 1062, when Archbishop Anno II kidnapped the young Henry IV. Emperor Frederick Barbarossa relocated the Rhine toll to Kaiserswerth in 1174 and had the palatinate expanded into a fortress, which was probably completed in 1193 under Henry VI. The current ruin dates from this period.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.zeche.org/
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: 51.2995, 6.7319