Where: Sankt Goar, Germany

Start of construction: 13th Century

End of construction: 15th Century

Most important renovation: 20th Century

Accessible: yes, museum and hotel

Important fact:

Taken and dismantled by the French army in 1797. Then became ruinous. Parts have been restored (and converted into a hotel) in the late 1990s, but the vast majority of the castle is still in ruins. The castle once had one of the tallest keeps of all Rhine castles (54m).