Visiting Toronto via it's underground walkway linking 28 kms of shopping can be daunting! So here below is the link, which will guide you from Union to Dundas Station and around. 

http://www.seetorontonow.com/insider/discovery.aspx

As per the Guinness World Records, the PATH is the largest underground shopping complex, which connects more than 50 buildings/office towers, 20 parking garages, 5 subway stations, 6 major hotels, and many more!