Foucault's pendulum swings from the center of the Panthéon's impressive central dome. The blurry gold ball is the "bob."
The pendulum in the Panthéon is the oldest surviving of Foucault's original pendula (that is an acceptable plural form!). The actual original, hanging in the museum of Arts et Métiers in Paris, was destroyed in 2010 when its cable snapped. There are many versions of the Foucault pendulum around the world. One of the more famous, and one that I saw as a schoolboy on a field trip, hangs (swings?) in the United Nations headquarters in New York City.