More northern cities like Montreal and Winnipeg also have very interesting indoor pedestrian systems. The one in Winnipeg is particularly useful, since there are approximately 72 hours per year that it's comfortable to be outside between the bone-chilling cold and the biblical swarms of mosquitos and flies in the summer.

https://en.wikipedia.org/wiki/Underground_City,_Montreal

https://en.wikipedia.org/wiki/Winnipeg_Walkway

My wife and I had a great time wandering around the Underground City when we visited Montreal. We were there in the fall, but it sunk in just how cold Montreal winters get when we went to a club that had a coatroom the size of my first apartment.