Free GM Resource: Perry-Castañeda Library Map Collection
This makes maps a great place to shave some GM prep time.
Whether you make your own maps or you like to borrow maps, the
Perry-Castañeda Library Map Collection from the University of Texas in Austin is a good place to start.
I have a friend who runs all of his games in a historical setting. He doesn't have to make maps, all he has to do is find maps from the proper era. One of his campaigns was set in Constantinople as it was during the crusades. It wasn't a crusade campaign, but that was the physical locale.
If you don't want to use the maps directly, they are still a good place to start when creating your own map. Starting with an old map as a source file is one way to go. Sometimes the old maps are just full of good little ideas that you can incorporate into your own map efforts to produce something unique, but with some classic styling.
I'm a huge fan of old English village maps because in my mind they do a good job of capturing the small-town low-magic RPG fantasy setting most low-level parties would be adventuring in. Of course village maps from any medieval country would probably suffice, but the English maps are the easiest for me to locate. If the University of Texas map collection doesn't have it, they most likely have a link to a collection that has what you are looking for.
This is a map of some English Village I "did up" for use as a base of operations for my gaming group. We never did use this village of Badger Falls, but I might use it someday. I removed everything that wasn't a road or waterway and added back in forests, houses, garden plots, etc.