Copenhagen is great destination for a day or weekend trip. The city is not so big and almost everything is walking distance. My 24 hours trip in Copenhagen was dedicated to visit some of the most famous tourist attractions in the town, try some local food, drink a coffee and walking down the streets with beautiful architecture.
Copenhagen is an interesting city where you can find a lots of good photography spots. My advice is to travel there in spring or summer because for sure is much better walking around without jacket and all that winter staff with you. We were there in March but we were lucky because it wasn’t so cold.