There are no lines at this former convent and no crowds: Few people even know it's here. What they're missing is one vast wall covered with the vibrant colors of Andrea del Castagno's masterful Last Supper (ca. 1450). Castagno used his paint to create the rich marble panels that checkerboard the trompe l'oeil walls and broke up the long white tablecloth with the dark figure of Judas the Betrayer, whose face is painted to resemble a satyr, an ancient symbol of evil.