There are several reasons why you would want to be able to find your save files if you are a Project Zomboid payer. Among the popular reasons, one is to generate backups that prevent progress loss in case saves are lost or corrupted. These backups are doubled as saves; you can get back to it at a later date for mere nostalgia or to check how much of progress you have made in the game. Certain third-party applications that let you change your game saves also need access to the save files. That is why it is important to know where your saved files are.
But the question should not be why you would want to access your game saves. Rather, it should be how you can access them. For your operating system, you can get help below:
Windows
On Windows, your Project Zomboid save files can be found in the following folder:
%UserProfile%\zomboid
To open that path, paste it into the address bar of File Explorer and hit ENTER.
Your character save is in the map_p.bin file, the other map_.. files are the map. Depending on your version and settings, these files may be within the zomboid folder itself, or a folder named saves, sandbox, or survival.
Mac
On Mac, your Project Zomboid saves are located in the following folder:
~/Zomboid
To open that folder, open Finder, press COMMAND + SHIFT + G on your keyboard, paste ~/Zomboid into the text field and hit Go.
Linux
When playing Project Zomboid on Linux, your save files will be placed into the following directory:
~/Zomboid