Around the corner from Langelinie and the Little Mermaid in Copenhagen lies the Citadel, a huge fortress originating from the 1600s.
It’s not just any fortress, it’s one of the best-preserved ones in entire Northern Europe. The construction of it was initiated already in 1626 by the King (Christian IV of Denmark) and has since then been used for protection during many invasions since then. Today, its still used somewhat by the military, however it mostly functions as a public park and of course, as a monument of cultural history. The Citadels is formed as a pentagram, and have a couple of old buildings still found inside. You’ll among others find the old prison complex, a church, and a windmill. The Citadel is a perfect place to stroll on a sunny day. The closest station is Østerport. Here’s a Google Map link of where to find the Citadel in Copenhagen.