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.
Pfostenschlitzmauer Pfostenschlitzmauer (German for "post-slot wall") is the name for defensive walls protecting Iron Age hill forts and oppida in Central Europe, especially in Bavaria and the Czech Republic. They are characterized by vertical wooden posts set into the front stone facing. The is constructed from a timber lattice filled with earth or rubble. The transverse cross-beams may also protrude through the stone facing, as with the "murus gallicus " used in Gaul and western Germany.