The Duomo di Milano took 579 years to build, making it one of history's longest construction projects. Duke Gian Galeazzo Visconti started it in 1386 hoping the Devil would stop haunting his dreams after he'd murdered his uncle. The entire population joined in, rich and poor alike, knowing they'd never see it finished. Visconti switched from brick to Candoglia marble, transporting blocks via canals from quarries near Lake Maggiore. Leonardo consulted on the troublesome dome in 1487. French architect Jean Mignot arrived from Paris in 1399 and declared everything built so far "in peril of ruin" because it was done "without science." He was wrong, though local architects forced the Duke to fire him anyway.

The cathedral holds the world record for statues: 3,400 in total. Gargoyles double as medieval rainwater drainage. The Visconti Viper appears throughout, commemorating nobleman Uberto Visconti slaying the dragon Tarantasio that terrorised Milan with its stinking breath. The gilded Madonnina crowning the tallest spire became so sacred that when modern skyscrapers exceeded her height, architects placed replica statues on their roofs out of respect. The façade wasn't completed until 1965.

VoiceMap's self-guided audio tours explain how Milan's canal network enabled the marble's journey, decode the hybrid Romanesque-Gothic architecture that infuriated foreign engineers, reveal Leonardo's role in solving construction deadlocks, and trace the Visconti dynasty's use of cathedral building to ease guilty consciences while keeping Satan at bay.