Kastellet

Kastellet - Credit: Wikimedia Commons

Kastellet (; ) is a citadel located in Copenhagen, Denmark. It is one of the best preserved fortresses in Northern Europe. It is constructed in the form of a pentagon with bastions at its corners. Kastellet was continuous with the ring of bastioned ramparts which used to encircle Copenhagen but of which only the ramparts of Christianshavn remain today. Read more on Wikipedia

type: military installation
date from: 1664
official website: https://forsvaret.dk/da/organisation/tjenestesteder/kastellet-i-kobenhavn/

Source: en.wikipedia.org