Brunelleschi's dome — completed in 1436 without scaffolding using a revolutionary herringbone brick technique — is Florence's defining landmark and one of the great architectural achievements of the Renaissance. The cathedral's striped green and white marble exterior is striking; the dome climb (463 steps, no lift) rewards with the finest panoramic view in the city.
Book the dome climb in advance. The adjacent Baptistery's golden mosaics and Ghiberti's bronze "Gates of Paradise" doors are worth separate attention; Giotto's freestanding Campanile is a less-crowded alternative for the view.