King Street West Railway Subway (Underpass) 1888
This railway underpass is one of the oldest in the City of Toronto. Rail lines were first built through this area in the 1850s, connecting Toronto to the upper Great Lakes and points in-between. By the 1880s, multiple tracks had been constructed to carry passengers and freight to destinations such as London and Chicago and, eventually, to the edges of the continent. Rail traffic was busy enough to cause lengthy stops and dangerous crossings for pedestrians and horse-drawn vehicles travelling between the City of Toronto and the Town of Parkdale. Designed by Charles Sproatt, a City of Toronto engineer, this underpass succeeded in solving the traffic problem, and was an important structure in the development of Toronto's rail and road system.
Plaque via Alan L. Brown's site Toronto Plaques. Full page here.