For centuries Brussels was surrounded by a grand 8km fortress wall. It was partly demolished in the 1790s, then removed altogether on Napoleon’s orders in 1810. Well, almost. In fact, a few isolated parts survived, including the Porte de Hal, one of the seven very imposing 14th-century gatehouse towers, which the French preserved for use as a military prison. The Porte de Hal was converted into a museum in 1847 and romantically embellished with statuary, windows and neo-Gothic turrets thereafter.
Today an audioguide leads you round its decent little city-history museum and exhibition of armour, and you can climb to the 6th-storey battlements.