1 day — Transit stop
Duomo (climb the rooftop!), Galleria Vittorio Emanuele II, Last Supper (if booked months ahead). One day is enough for the essentials if Milan is a stopover.
2 days — The real Milan
Add: Brera district + Pinacoteca di Brera, Navigli canals for aperitivo, Fondazione Prada. Two days reveals why Milanese love their city.
3 days — In-depth
Add: Castello Sforzesco, a day trip to Lake Como (1hr by train), Porta Nuova modern architecture, the Cimitero Monumentale (outdoor sculpture museum — free, extraordinary).
4+ days — Milan as base
Add: Bergamo (stunning hilltop town, 50 min), Pavia Certosa, outlet shopping at Serravalle, an evening at La Scala opera. Milan is an underrated base for Lombardy.
Our recommendation: 2-3 days
Book the Last Supper (Cenacolo) the moment you decide to visit Milan — it allows only 25 visitors every 15 minutes and sells out 2-3 months ahead.