You do not state what platform you are playing on, but I am guessing it is some flavor of the PC/Windows Java-based version of the game. Save games show up in different places, depending upon your platform (Java, Win10, PE, etc).
When the Minecraft launcher opens up, edit the profile you normally use to play your world. It will show you the directory where the profile saves its worlds. Look in that directory for your saved worlds. The name of your world is usually the same as the directory name, but as others have stated, if you rename your world in the game, it does not rename the directory holding the world.
If really in doubt about which directory contains your saved world, figure out which directory your profile is using. Then play the world you are looking for and quit the game. Using your computer's file browser and navigate to the saved directory for the profile. The saved world directory that was most recently modified will be the one you just played, and the one that contains the world you are looking for.