Big enough to hold 4,000 worshipers, and breathtaking in the richness of its interior furnishings, this magnificent structure was designed in 1824 by James O'Donnell, an Irish-American Protestant architect from New York. So profoundly was O'Donnell moved by the experience that he converted to Catholicism after the basilica was completed. The impact is understandable. Of the hundreds of churches on the island of Montréal, Notre-Dame's interior is the most stunning, with a wealth of exquisite detail, most of it carved from rare woods that have been delicately gilded and painted. O'Donnell, one of the proponents of the Gothic Revival style in the early decades of the 19th century, is the only person honored by burial in the crypt.

The main altar was carved from linden wood, the work of Victor Bourgeau. Behind it is the Chapelle Sacré-Coeur (Sacred Heart Chapel), much of it destroyed by a deranged arsonist in 1978 but rebuilt and rededicated in 1982. The altar was cast in bronze by Charles Daudelin of Montréal, with 32 panels representing birth, life, and death. A 10-bell carillon resides in the east tower, while the west tower contains a single massive bell. Nicknamed "Le Gros Bourdon," it weighs more than 12 tons and has a low, resonant rumble that vibrates right up through your feet. It is tolled only on special occasions.

Although you can go through on your own, there are guided tours in English at various times throughout the day, beginning with one at 9am. There are sound-and-light shows nightly Tuesday through Saturday.