For all the time spent commuting on the TTC, we tend to forget just how fascinating complex transit systems can be. Part of the reason for this, I suspect, is that we don't know about all the hidden spaces and clandestine features that surround us every time we take a ride on the subway.

From abandoned passageways to PA codes, here are some fascinating secrets of the TTC.

1. There's a walled off passage between the two sides of the platform at St. Patrick Station that was the site of a murder in 1975. This is also why there's a jail-like area at Museum Station.

2. Both Keele and Woodbine stations on the Bloor-Danforth Line feature hidden passageways to what were once connecting streetcar loops when each station served as the terminus of the line during construction in the 1960s.

3. "299 Bloor Call Control" is a PA code for a supervisor / line mechanic. You check out all the various codes over at Transit Toronto.

4. There's an enormous attic at Lawrence Station above the north escalators that resembles something from a Kafka novel with numerous rooms, tunnels, and passageways. Aside from TTC staff, only a few urban explorers have gained access.

5. Somewhat similarly, there's an abandoned subway entrance at Queen Station that you can just see a peek of when you look down the grate on the north side of Queen just east of Yonge (look for the light coming from the crack in the door of the station).

6. The mysterious geometrical symbols on station platforms have important purposes. The red circle helps the driver position the train properly in the station, while the green circle(s) are used by the crew member operating the doors as part of a "point and acknowledge" system to prevent the doors opening before the train has stopped.

7. The TTC plays classical music at some stations to discourage loitering on the part of our youth. Apparently it works.

8. While the TTC once tried to use a logical numbering system for all of its routes, it ceased to be predictable long ago. Now it's just a mess of different schemes that have been blended together.

9. Spadina is actually two subway stations. The northern portion of the current station, separated by a 150 metre walkway, was once to be named Lowther and only accessed from Line 1. The TTC changed its mind and linked them before Lowther ever opened with that name.

10. There's a spare centre platform just sitting there at Sheppard-Yonge Station. The idea was to have passengers enter and exit from different sides of the train, but the ridership never warranted bothering to do this.