That's where their pool is. There's a publicly-accessible area to the right of the red circle that wraps around the office building; it's a nice quiet spot to have a sandwich on your lunch break.
I would hate this building a lot less if it wasn't right fricken across Nathan Phillips. That land had so much potential *sigh*. Even something at 100m that haad an interesting shape would have been 100 times better. Now I can only hope for the day that the low rise part of the Sheraton is demolished for something that spices up the city. The south part of Queen St from Bay to University is one of my least favorite places to walk.