Viking Ring Fortress, Trelleborg/ trelleborg a collective name of circular forts in Denmark and southern Sweden. 5 are dated to the reign of herald Bluetooth first discovered example named after trellebrog near slagelse,denmark.
Stevns Klint chalk cliffs in Zealand, Denmark. There is a fort located here (of cause) from the cold war - overlooking the Baltics one could keep an eye on the east. Now it is just a fun museum, and a great place for a hike :P