“Imagine a city where graffiti wasn’t illegal,” the anonymous British graffiti artist Banksy once suggested, “a city where everybody could draw whatever they liked.” And what if one could draw on the hallowed walls of a 16th-century building? In this 100-work exhibition, Donato Bramante’s Chiostro from the 1500s is the setting for Banksy’s fiercely contemporary messages, ideas, and dreams. The exhibition includes book and record covers, works on paper and canvas, and stencils on metal and concrete. —E.C.