This was intended to allow TTC streetcars to run the length of Queen Street, but keep them underground, thereby reducing traffic. It was to run from Trinity Park in the west to Carlaw Avenue in the east.
Digging was already being done for the Queen Subway Station on the Yonge line, so it was decided to excavate the intended streetcar station at the same time.
Shortly afterward, however, a decision was made that moving the east / west corridor to Bloor made more sense given the volume of traffic. It was further decided that a subway would better meet the needs of that traffic than streetcars. As a result, the project was scrapped.
I have to admit, this wasn't as impressive as Lower Bay and yet it was very interesting just the same. The size of the support beams was impressive. Some of the ceiling beams were clearly original to the construction of the Queen station.
It was apparent that few of the public ever see this place, and it has de-evolved to being a mere mechanical room. However as you look at the two parallel track beds running the length of this large area, you can't help but imagine one of the old-style streetcars gliding through to the sound of metal on metal wheels.