Put Old Montréal and the Old Port at the top of your sightseeing list. Spend a full day walking around this area, head back to your hotel for a late-day break, and return for dinner. Aside from finding several of the city's top restaurants here, City Hall, Marché Bonsecours, and other charming buildings are illuminated at night. Also dedicate a full day to wandering around Downtown, rue Ste-Catherine, and Chinatown. Visit the Latin Quarter and the area around McGill University—both have a busy student life, but shouldn't be dismissed as places where only under-20s frequent. Even if you're too tired to go out on the town, take a nighttime walk down rue Crescent or rue St-Denis for a taste of the city's joie de vivre.
For browsing, shopping, and dining out, explore Outremont, Mile End, the Plateau, and Westmount. For kid-friendly activities, check out Hochelaga-Maisonneuve and the Islands for the Biôdôme, La Ronde, and the Jardin Botanique.
And a city landmark not to miss is St. Joseph’s Oratory, Canada’s largest church. It’s on the west end of the city, which makes it a little out of the tourist area, but it’s worth the trip.