When walking the grounds of Trinity College in Dublin, you'll encounter several pieces of public art. To me the most interesting of these was situated just outside the Berkeley Library, close to the main Trinity College Library (in which resides the Book of Kells). This bronze artwork, by Italian Arnaldo Pomodoro, is titled 'Sfera con Sfera' (sphere within a sphere).
The 'Pomodoro sphere', as it is known locally, was donated by the artist. Similar spheres can be found in a variety of other sites, including the United Nations plaza in New York, U.C. Berkeley, and the Vatican Museums. As the name implies, there is a sphere that rotates within a larger rotating sphere.