The Old Port stopped being a working port decades ago and became the city's front porch — three kilometres of quays along the St Lawrence, anchored at one end by a clock tower and at the other by a silver dome. Best on a clear afternoon; in rain it's a long flat slog with nothing overhead, so wait for the weather.
Start under the dome of Marché Bonsecours and drop down to the water, then walk east to the Quai de l'Horloge, where the 1922 Clock Tower stands as a memorial to sailors lost at sea — climb it if it's open. The urban beach at its foot is for sitting, not swimming. Track back west along the promenade past the Quai Jacques-Cartier and the Ferris wheel turning over the basin.
The last quay, King-Edward, gives you the whole port in one sweep, and across the water you'll see Habitat 67, Safdie's stacked concrete from Expo. You can't easily walk to it; this is the view. Cut up into the city and Square-Victoria-OACI takes you home.