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Lower Queen station in Toronto is the real centerpiece of abandoned stuff on the TTC. Way back before we were even talking about a Subway on Yonge Street the idea was for Queen Street to be the main artery for Streetcar routes into the downtown core. So the idea was to run the streetcars underground starting just outside of the downtown core (think of the Streetcar "subway" in Boston). Amazingly this plan lasted right up to the design and construction of the Yonge Subway in 1954. Obviously however the Streetcars never made it underground along Queen even though a station for them had been constructed under Queen Subway station.
Lower Queen may have found use however if the Bloor-Danfoth Subway was built as originally planed from Woodbine to Keele via Queen Street, however this didn't happen either. Today Lower Queen is home to nothing but some ventilation, a pedestrian path to cross under he Subway platforms and an elevator shaft.
Also of note is Osgoode Station (Queens opposite to the West) had its utilities relocated when the University extension was constructed in the late 60's for a potential Lower Osgoode Station. This shows that even into the mid 1960's the city believed that there would be a Subway under Queen Street at some point. Jump to today and the plan for the DLR Subway line has it running under Queen street with a stop at Queen Station and Osgoode Station. Since Lower Queen can no longer support a Subway the DRL will have to dig below it (guess will call that station Lowest Queen), however I think will be thanking the gods that we won't have to do utility relocation under Osgoode Station since that was done in the 60's.