Free Tours with a Local
An organisation called Global Greeter Network http://www.globalgreeternetwork.info provides free tours with a local guide in cities around the world. Not every city offers the service yet, but many including New York, Calcutta, Moscow, Florence and a large number of lesser-known cities do.
The concept originated in New York, and is spreading throughout the world. It is purely non-commercial, and gives you a chance to meet a friendly local and see the locale through their eyes. They may take you to visit their favourite pastry shop, tell you about little known sights of interest, or offer you a walking tour of their neighbourhood.
This sounds like a fabulous idea to me. I checked and it is not yet available in Montreal. If it interests you and your city does not have a group yet, you can apply to organise one provided you have four friends willing to participate. If a group already exists, you can apply to be a greeter.
It is definitely something I will look into the next time I am in an unfamiliar city. I learned about the group through a story in my old newspaper, The Globe and Mail http://www.globeandmail.com.