MAXXI is Rome's national museum for contemporary art and 21st-century architecture, housed in a sweeping Zaha Hadid building north of Piazza del Popolo. The architecture is part of the reason to go: concrete curves, ramps, bridges, and galleries that feel very different from Rome's usual stone and stucco.
The exhibitions change, but the museum is a strong choice when you want to see modern Rome rather than another layer of the ancient or Baroque city.