This magnificent tower fort, built between 1845 and 1847, is surrounded by a moat for extra protection. Fort Asperen last saw active use on 12 April 1940, as part of preparations for the coming war. However, the Germans flew straight past it. Fort Asperen, which is an artwork in and of itself, is open to visitors in the summer months. The domed roof to keep out the rain, for instance, is made entirely of glass slates designed in the Glassworks at the National Glass Museum.