The first Trizec-constructed project was THE SHOPPING PROMENADE, which was 2 fully-enclosed concourses of stores installed beneath Montreal's 617 foot-high PLACE VILLE MARIE skyscraper. 

Dedicated in September 1962, PLACE VILLE MARIE was the first segment of Montreal's present-day UNDERGROUND CITY. Consisting of 1,600 stores and services, and extending for a total of 20 miles, it is the largest subterranean retail complex in the world.
Photo from Wikipedia / "Montrealais"