Sometimes after you finish a day, a baby penguin will pop up on the side of your screen. Simply click on all 4 to collect the achievement.
Easter Egg Spoilers:
*** Spoiler - click to reveal ***Clicking the penguin will bring you to a YouTube video. There are 4 videos, all of them short and playful interviews or reviews about the game from characters like baby penguins. You don't need to watch the videos for the achievement, but why not? Cute little penguins and humor are worth it.