Kastellet. The well-preserved remains of this Copenhagen citadel are one of of the kinds of fortresses that used to be littered across the continent of Europe. The Citadel - (Kastellet) was first established as a Garrison by King Christian IV The fortress is Europe's oldest military bastion and still in operation. King Christian IV ( - ruled Denmark and Norway ) had also planned. Denmark · Kastellet The Citadel Copenhagen. With David Ebershoff in The Danish Girl. .. Copenhagen: capital of Denmark - Europe's cool and green city. Kastellet (The Citadel) in Copenhagen is one of the best preserved star fortresses in Northern Europe. The Citadel was constructed from by Danish King. Visit one of Europe's best preserved city fortresses, Kastellet (The Citadel), right at the heart of Copenhagen and next to The Little Mermaid. Download this stock image: Gate at Kastellet Citadel in Copenhagen, Denmark, Scandinavia, Europe - bctf05 from Alamy's library of millions of high resolution.