Coal Harbour Community Centre is built into the slope from West Hastings Street down to the seawall. Its roof, level with the street, is home to paths, lawns, and a children's playground, as well as this windowed structure. If you look in the windows, you can see straight down into the Community Centre's public area. It looks (to me) a little like the sail of a submarine, in keeping with the building's overall vaguely nautical-themed architecture.
Post title from this song by Whitley.