The last remaining part of the second city walls of Brussels, the Porte de Halle (FR) / Hallepoort (FL) / Halle Gate (EN) is now part the Royal Museums of Art and History, ergot Ah, Royalty material. It was originally built in the 1300s, same general time frame as the Keep at Vincennes. It’s been remodeled often since. I happened past it during my walk to the train station after some meetings in Brussels back in April.
(so much world, so little time....) 