Every year Tivoli dresses up for Christmas. It's an orgy of light in the darkest time of the year. It's a Christmas market where people are selling hot chocolate, mulled wine, æbleskiver, and candy. Others sell ornaments and other Christmassy things. It's a magical place, and there's no way that you can leave there without being in the Christmas spirit.
Swans in front of Nimb
The Japanese Tower
The Russian Christmas tree
Tivoli in the summer is amazing. I've heard it's fantastic at Halloween. But Tivoli at Christmas is just spectacular. I can't recommend it enough if you ever visit Copenhagen or Denmark in December.