Jugendstil, Art nouveau, Skønvirke etc.
This special era is called by many names. I love this art and architecture movement, that humanised what had become dehumanized by the industrial revolution.
Flensburg has many beautiful Jugendstil buildings, and you can get a fine introduction at Museumsberg, also to the Jugendstil painter Hans Christiansen (1866–1945) who was born in Flensburg.
You find a map at Museumsberg, and on the buildings. Most of them are located at Am Burgfrie, Nikolajstraße and Toosybüystraße.
My mobile phone pictures don't do justice. You have to get close to see the wonderful details