While traveling for side-quests, bobbleheads, behemoths and everything else in the game, you should get this achievement with little effort. If you reach level 20 and need some help, take the "Explorer" perk. This will show you the locations on your map but still allow you to "discover" the locations.
Note for PC Users: If you have used the "tmm 1" code to show all the locations, you will not receive credit for finding the places when arriving at them. All you have to do is open the console back up and type "tmm 0" to turn the locations off. Once you exit the console you will "discover" whatever location you're standing in. Type "tmm 0" again to hide that location and you will again discover it when you close the console. Repeat this process until you have "found" that same location 100 times.