The Toronto Eaton Centre has many interesting features. As was mentioned by Avatar-X
1) Huge underground loading docks. Yes it does. A veritable highway that stretches the full length, north-to-south. People get around in electric golf-carts as in some James Bondian underground lair. Many of the larger doors open when a light beam is interrupted - so that the carts can travel unimpeded. These emitter/reflectors are high enough to crawl under on ones belly or hurdle over. Unless you let your leg drag and then be prepared for a scare of a lifetime.
2) Service corridors and freight elevators. There are many side hallways (back entrances) for the supplying of the retail stores. Many corridors - some quite narrow, dark, and claustrophobia inducing. Others are airy and have a cat-walk structure overhead for quick hiding from security. Freight elevator goes down to garbage level - garbage bins and the like. Scout it out and it becomes invaluable information if anyone asks where you're going and you need a plausible destination. You'd be surprised at how accommodating people are - even offering to push the correct floor buttons for you.
Also there are the following:
3) Interesting intertwined staircases in the south-west part of the building. Glassed in enclosure offers vistas to the outside. The stair case appears normal until you realize the one you're on is not the same as the one you see scissored across from you. You need to jump over the railing... the alternate universe one goes to all the floors that were heretofore inaccessible. Doors are usually locked though. A small access port in the wall on the top floor is a way into the elevator shaft if you are so inclined. Also locked but some ingenuity might gain you access. Nothing to see here.
4) The magnificent glass dome can be traversed if you are brave. From the Yonge St (east) side over to the west. Unfortunately the west side does not have much of a foothold except a narrow ledge... so I could never muster the nerve to climb down that slope. I did drape myself on the very top and peer down through the class. Best do this against a night sky lest shoppers point and stare. This was approximately overtop of the passenger elevator - near the fountain. Pick a non windy and non cold night and be smarter than me. Discontinuous roof areas are very interesting around that area as well where one overlooks a landlocked church roof. Some bravery and lack of acrophobia a must.
5) The spiral car ramp which services the outdoor parking levels - winds itself around a hollow core which may be entered from the very bottom. There is a submarine type door - and for all I know it may be locked by now. But there is a security camera just opposite. Bummer. This concrete cylinder is fascinating place to rest within if you get the chance. Friend and I noticed several golf balls which we stupidly tried to fling straight up - hoping they'd go over the top edge. Do you realize how hard it is to throw something straight up? How did those golf balls get there? Our guess was that some bored execs spend their time practicing their swings from adjacent high-rises and this core is their 'hole'.
6) Access grates in the sidewalk around the Centre... basically telephone and electric. These have been reinforced-locked over the years. Rungs lead you straight down to a low-ceiling tunnel system that ends up in a switching room. Easy to get lost though since things branch off. They used to offer unimpeded 24-7 access to the Centre at off hours. Perhaps they may now only be explored coming from the other direction.
Disclaimer: the information may not be current and represent findings from the 80's. Therefore they may not be accurate today but should still serve as a guide or as a catalyst for new ideas.