Once an active station on the subway system of Toronto, if only briefly, the lower level to Bay station has the honour of being the only completed and usable station in the system to sit unused, never seeing the public traffic that the other stations see daily. Being out of sight, it is also out of mind for many citizens of the city and those who pass over it daily.

Bay Lower, which was designed by architect Arthur G. Keith, was built at the same time as the rest of the Bloor-Danforth line (green line), when there were plans to interline trains on the Yonge-University line (yellow line). It saw use for six months before it was determined that there were too many issues with the interlined system, of which signaling and train scheduling issues were the most common, and the two lines were separated.

Construction of the Spadina line in the late 1970's dashed any hopes of restoring the interlining system... extending from St George Station northward past the original connector tracks between the two lines, any attempt at interlining now would be extremely complicated and impractical.

Bay Lower (as the lower level is referred to by both the TTC and transit enthusiasts), no longer needed, was sealed off for the most part from the station above, and relegated to its current use - staff training (both TTC and Toronto Police Services) and movie shoots. The connector tunnels remained in place, as they are used by the TTC to shuffle equipment between the two lines. As well, when the stairwells were entombed on the upper level, a different tile was used that that of the station walls, making it obvious where the stairwells to the lower levels remain inaccessible save for locked doors in the walls.

Glimpses can be caught by looking out the front of the trains, slightly to the left, as the depart westbound from Yonge Station, although this privilege may not last too long... the new subway cars do not offer the "railfan" window, and while they will first appear on the Yonge-University-Spadina line, they will invariably make their way to the Bloor-Danforth.

There used to be a time where entering the connector tunnels from Museum (the connectors tunnels that terminate at Yonge would require entering from Yonge Station, which is far too busy for this task) and following them would give one access to the station. While this is still the case, it is also likely to give one access to the back of a police cruiser. The presence of security cameras on the platform have been confirmed at Doors Open Toronto events in the past, and rumours of motion sensors in the tunnels occasionally appear on internet forums.

These days, with the station having been locked down so, the only real way down there now is during one of the infrequent tours offered by the TTC, or at any other event where it is open as a venue.