If you find yourself in Toronto on a rainy day or a Wednesday evening (admission is free every Wednesday evening), stop by the Art Gallery of Ontario. It's centrally located near Kensington Market. Of course they have some great art, but what sets this museum apart is the unique design. In the lobby, there's a very interesting spiral staircase that will wind you up many floors to the very top. Stay for a bit at the top to see a great skyline view of the city.
I'd normally recommend skipping the overprices museum cafe, but this one is very interesting. It's on the side of the museum on the second floor with a great view of rowhouses. The design is wooden and makes you feel like you're in a belly of a whale. It's awesome!