Discovering a secret level in a video game is like discovering pirate's treasure, only without the monetary gain and cool Captain's curse.
These are the levels that keep gamers talking, the secret spaces that give us a reason to replay a game until we've discovered every pixel of that virtual world.
WatchMojo put together a nice list of their picks for Top 10 Secret Levels In Video Games to put you in a nostalgiac mood.
From Super Mario World's fabled Star Road to the ridiculous Secret Cow Level in Diablo II, these are levels that "are hidden and must be found by completing certain objectives or searching certain areas of a game", a gamer's ultimate prize for playing.
-Via Geeks Are Sexy