The Chicago Postcard Museum

You can't go there physically, the museum is here. Like a good history or a photo album or a museum exhibit, it's unlikely that your ancestors will pop up here (although since the proprietor includes the message sides of the postcards, it's possible!). What you will get is some perspective on how the city used to look -- at least the parts the buyers and sellers of postcards cared to commemorate. I'm fond of this image of the produce market on South Water Street west of State but got a headache trying to figure out which high-rises have their footprint there now.

The images may be downloaded free provided that the downloader gives credit or a hyperlink to the museum.