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.
Fort Friedrichsburg Fort Friedrichsburg or Feste Friedrichsburg was a fort in Königsberg, Germany. The only remnant of the former fort is the Friedrichsburg Gate (Russian: Фридрихсбургские ворота , German: "Friedrichsburger Tor" ) in Kaliningrad, Russia.