Built in the early 20th century, during the days when Poznan was a German outpost known as Posen, the castle once served as a residence of Kaiser Wilhelm II. In the late 1930s, the interior was refurbished as quarters for Adolf Hitler. Within the walls of this imposing neo-Romanesque building, Polish cryptologists worked to decode the Enigma Machine, the main secret-code generator used by the Germans. Their work contributed to the Allies' victory in War World II. In the clock tower, you can walk into the rooms done in the Third Reich style and look out of the balcony that was intended for the Fuhrer to inspect military parades. As the castle is still seen as a symbol of foreign domination (a fate shared by Warsaw's Palace of Culture), locals are ambivalent toward it. After World War II, there were talks of demolishing it, but pragmatism for office space kept it standing. Today, it houses the Castle Culture Center (Centrum Kultury Zamek), which hosts exhibitions, theater performances, and concerts, and screens films. A quick visit will take no more than 30 minutes. You can use the exhibitions as an excuse to see the castle's interior, notably the golden mosaic ceiling on the clock tower's ground floor. However, the Kaiser's marble throne can be seen only with a guide on Wednesdays at 6pm.