The remains of the Castle can be visited
Andernach Castle

Andernach Castle Ruin, also known as the Electoral Castle, is a Romanesque moated castle with later Gothic and Renaissance elements. Originally built in the late 12th and early 13th centuries, this complex is among the best-preserved ruins on the Middle Rhine, despite its destruction during the Nine Years' War.
History+
The planning and construction of Andernach Castle began under Archbishop Rainald von Dassel, who received Andernach from Emperor Frederick I in 1167. The castle served as the southernmost outpost of Electoral Cologne and was erected by his successors Philipp I von Heinsberg, Adolf I von Altena, and Bruno IV von Sayn at a location. Officially, it was intended to protect the nearby castle gate and the Rhine customs, but its primary purpose was to control the citizens of Andernach, who repeatedly sought independence.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Stadtburg_Andernach_1.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: 50.4392, 7.4050