What Fortress used as a palace and prison has the Festning tunnel running underneath it?
Akershus Fortress Akershus Fortress (Norwegian: "Akershus Festning" ) or Akershus Castle (Norwegian: "Akershus slott" ) is a medieval castle that was built to protect Oslo, the capital of Norway. It has also been used as a palace and as a prison.
Poznań Fortress Poznań Fortress, known in German as Festung Posen (Polish: "Twierdza Poznań") was a set of fortifications in the city of Poznań (German: "Posen") in western Poland, built under Prussian rule in the 19th and early 20th centuries. It represents the third largest system of its kind in Europe.