Beneath Line 2's Bay station is an abandoned second set of platforms, commonly referred to as "Lower Bay". They opened in 1966 as part of the Bloor-Danforth Line and the extra platforms allowed a hybrid route that combined with the University Line to loop around downtown. It caused a lot of confusion and the plan was scrapped after only 6 months.
While it only lived a short life serving transit passengers, Lower Bay has been used for media productions and opens rarely, such as during the annual Doors Open event.