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Covering 2.3 sq km, North America's largest fort was begun by the French in the 1750s and completed by the British in 1850, intended to defend against an American invasion that never came. A one-hour guided tour takes in the regimental museum and numerous historical sites. Summer-only events (late June through early September) include the changing of the guard (10am daily) and the beating of the retreat, which features soldiers banging on their drums at shift's end (6pm on Saturdays).
Today the Citadelle is the base of Canada's Royal 22s (known in bastardized French as the Van Doos, from the French for 22, vingt-deux). Founded in WWI, the regiment earned three Victoria Crosses in that conflict and WWII. Tours depart at least once per hour year-round, with French- and English-language tours alternating throughout the day; call ahead for schedule information. From late June through October, lantern-lit evening tours (adult/youth $20/16) are also offered.