For me, maps are perhaps the best form of recreational reading ever ... and that's particularly true of historic maps. So much intriguing information packed onto a single sheet of paper.
And for anyone interested in local history, old Sanborn maps are by far the most intriguing things to browse. Sanborn maps were mostly created in the late 19th and early 20th centuries, and designed to be used by companies that sold fire insurance. They're an amazingly detailed snapshot of a town, showing the location, size, materials, and use of every single building in the map area -- an unparalleled resource for historians.
Back in the day, Sanborn maps were created for over 200 Montana communities ... including a number of frontier towns that don't even exist anymore. The originals were in color, but you can find black-and-white versions of all of them on the internet with a little digging and password-searching. Once you do, you'll likely be hooked for days.
Here's a small snippet of one of the old Sanborns ... this one showing how a part of the coal mining town of Bearcreek looked back in the summer of 1914: