Fort York
Fort York constituted the primary defensive position in early York (Toronto). The present buildings, erected between 1813 and 1815 to replace those destroyed during the American occupations of York in 1813, are among the oldest in Toronto and are important surviving examples of British military architecture. At the turn of the 20th century, the fort was threatened with demolition. The fight to save it led to one of the first victories of the Canadian heritage movement. The fort was bought by the city in 1909 and restored between 1932 and 1934 as part of Toronto's centennial celebration.
Plaque via Alan L. Brown's site Toronto Plaques. Full page here.