Here is a little bit of history on it:
The foundation stone of Cologne Cathedral was laid on August 15, 1248, by Archbishop Konrad von Hochstaden, and the choir was consecrated in 1322. After this initial rapid progress, construction work gradually came to a standstill, and by the year 1560, only a torso had been built.
Only with the 19th century Romantic enthusiasm for the Middle Ages and the commitment of the Prussian Court did construction work resume. 1824 saw the addition of the towers and other substantial parts of the cathedral, mostly according to surviving medieval plans and drawings.
The completion of Germany's largest cathedral was celebrated as a national event in 1880, 632 years after construction had began. The celebration was attended by Emperor Wilhelm I."
Thanks to a good friend of our family's, Mrs. McKinnen, here is a little story about the cathedral from WWII: