XNL Piacenza, the former headquarters of the Enel Electricity board, is now a cultural center for contemporary art. An early-20th-century structure, the building is an important city landmark. To celebrate its new purpose, 150 works are on display, drawn from Italy’s 18 most important art collections. Among the exhibitors: Maurizio Cattelan, Marina Abramović, Tomás Saraceno, Andy Warhol, Bill Viola, Dan Flavin, and William Kentridge. An ode to the city, the show is especially meaningful given Northern Italy’s recent battles. —E.C.