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.
Svartholm fortress The Svartholm fortress (Finnish: "Svartholman merilinnoitus" ; Swedish: "Svartholms fästning" ) was built between 1749 and 1764 outside Loviisa in Southern Finland by Augustin Ehrensvärd. The fortress, which lies at the mouth of the Bay of Loviisa, along with the planned land fortress at Loviisa, would have prevented invading Russian forces from entering what was then Swedish territory in present-day Finland.