When you walk to the Moderna Museet on the beautiful island of Skeppsholmen, you will see some big, very colourful sculpures and some sculptural machines. This place is called "The fantastic paradise" and the sculptures are made by french-swiss artist Niki de Saint Phalle and swiss sculptor Jean Tinguely. Niki is most known for her "Nana"-sculpures. You can find some of them in the garden, among with some of Jean's sculptures.
You might already have seen some of their work when you've been travelling. There is for example the Stravinsky-fountain in Paris or "L'ange protecteur" in the big hall of the railwaystation in Zurich, Switzerland. While in Stockholm, I really recommend you to take a walk at Skeppsholmen and have a look at those sculptures.