Blåtårn
Denmark
The 186th tallest tower in the world
Blåtårn (in English: Blue Tower) was a tower in Copenhagen Castle, the Danish royal family's palace in Copenhagen, Denmark. The tower was used as a dungeon and has been known as such in history. It is not known when the tower was built, but it is known to have existed during the reign of King John I of Denmark (reign 1481–1513). It existed from at least the late 15th century until destroyed in 1731–32.
Building data from Wikidata (CC0); heights normalised. Summary from Wikipedia (CC BY-SA).