's-Hertogenbosch, Italy
This fortress was added to the city later and is not directly included in the fortifications but sort of pasted on. It held the garrison to protect the city or, if necessary, to counter an uprising in the city. It is now part of the national archive.
Listen to the audio guide for Citadel van 's-Hertogenbosch Free on WIP — starts by itself when you arrive, even with the screen off