Kastellet was designed concerning 1662 and 1725 and was a cornerstone of King Christian IV’s defenses of Copenhagen. It remains to be in use by the army and inside of you can find long, crimson brick, slate-roofed structures, a parade ground, and in many cases a Dutch-design and style windmill. https://econopass.com/travel/10-must-see-and-do-in-copenhagen/