The Castle can be visited
Stolzenfels Castle

In the Koblenz district of Stolzenfels, Stolzenfels Castle stands, a structure that was transformed into a Neo-Gothic palace in the 19th century. Originally, it was a 13th-century customs castle.
History+
The origins of Stolzenfels Castle date back to the 13th century, when Archbishop Arnold II of Isenburg of Trier had a hillside castle built between 1242 and 1259. The five-sided keep was constructed in 1248. Under Archbishop Baldwin of Luxembourg, the complex was expanded around 1300 into a Trier customs castle and connected by walls to the town on the Rhine bank. Later additions by Archbishops Kuno and Werner von Falkenstein included a residential tower and a palas on the Rhine side. During the Thirty Years' War, the castle was occupied multiple times and destroyed by French troops in 1689 during the War of the Palatine Succession, after which it lay in ruins for over 150 years. In 1815, the city of Koblenz presented the ruins as a gift to the Prussian Crown Prince Friedrich Wilhelm, later King Friedrich Wilhelm IV, who accepted it in 1823.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=614
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: 50.3033, 7.5923