Palazzo Madama is a 16th-century Medici palace just north of Piazza Navona. Cardinals Giovanni and Giuliano de' Medici lived here before becoming Popes Leo X and Clement VII, and Catherine de' Medici stayed in the palace before her marriage into the French royal family.
Since 1871 it has housed the Italian Senate, so most visits are about the exterior and the political weight of the place rather than casual wandering inside. It is still worth a look while walking between the Pantheon and Piazza Navona.