Medemblik on Monday: see the castle outside, visit the museum another day
Radboud Castle has a medieval story, but is closed on Monday 19 October. The waterfront and old town still invite a walk.

Radboud Castle is a landmark on the Medemblik waterfront. It was built at the order of Count Floris V as one of five castles in West Friesland between 1282 and 1287. According to the castle itself, it is the last survivor of that group.
Inside, the museum displays objects about the building’s origins and history. Anyone hoping to enter on Monday 19 October must wait: normal opening runs from Tuesday through Sunday. For later in the week, the official site lists 11:00 to 17:00, with the warning that it may close earlier on quiet days.
There is more to Medemblik than the castle. The regional tourism site mentions the harbour, Bonifacius Church and museums including the Bakery Museum and Steam Engine Museum. The opening hours of those museums were not checked for this day in the source file; consult their own sites before planning a visit.
Nor should a Monday trip on the Hoorn–Medemblik heritage steam tram be assumed. The retrieved calendar shows services on 24, 25 and 31 October and 1 November, but none on 19 October. The journey planner shows the current departure times. Radboud Castle is at Oudevaartsgat 8.