"Akershus Fortress () or Akershus Castle () is a medieval castle that was built to protect Oslo, the capital of Norway. It has also been used as a prison."@en . "Stone"@en . . "Norway"@en . . "Akershus slott og festning"@en . . . "1290"^^ . "Akershus Fortress () or Akershus Castle () is a medieval castle that was built to protect Oslo, the capital of Norway. It has also been used as a prison."@en . . "Oslo, Norway"@en . "Akershus Fortress"@en . . . . . "Akershus Castle and Fortress"@en . . . . . . . . . . . "1290.0"^^ .