Den Helder still shows remnants of being a fortress in the late 18th and early 19th centuries. If you look at a map (even on your phone), you can still see the star-shaped moats in the north of the city. Some are visible by walking around the sea-wall, but are not as well preserved as Naarden.
Den Helder is the beginning of the train connection in the direction of Alkmaar and Amsterdam . Every half an hour an intercity train leaves from Den Helder to Amsterdam. This train stops at all stations between Den Helder and Alkmaar. The train from Amsterdam Centraal is roughly 1 hour and 30 minutes.
Visit: Museums and other things to see in Den Helder are: