I've actually never been, but saw it featured in a CanCon movie, waydowntown, where a group of office workers wage a month's salary as to who can stay inside the longest:
https://en.wikipedia.org/wiki/Waydowntown
Fellow Calgarian here. I like how the term "plus 15" refers to any elevated path in Calgary. For example, the link between the new cancer centre and Foothills Hospital is often referred to as the Plus 15.
Called the +15 because it's 15 feet above ground