Montreal has a huge series of interconnected underground malls.  For some
amazing details, see <a target=_blank
href="http://www.fodors.com/miniguides/mgresults.cfm?destination=montreal@106&cur_section=fea&feature=30006">Fodor's
description</a>.  Since it was such a nice day, we only explored the 
underground briefly.  But the extent we saw was still impressive.  This 
picture shows that at some places, the underground city had many floors of 
stores. <br>
We also noticed that, unlike at Complexe Desjardins, everything was open.