Game developers have been hiding secrets in their games since 1979's Adventure. But the inclusion of secret levels in games is a bit more rare, as it means hiding away tons of content (which takes time and money to produce) where many players will never find it. These levels are often snapshots of abandoned or forgotten content, tantalizing players with mystery and sometimes downright creepy additions to a familiar world, or just Easter eggs meant to satisfy the secret-hungry player.
Hidden levels in video games exist outside the main content of a game, meaning you'll have to dig a little deeper to find them. Whether that means glitching through a wall, entering a particular button combo at the right time, or venturing far off the beaten path, you'll have to look hard to find what developers are hiding in your favorite games.
Whatever the reason behind their inclusion, players delight in finding entire new secret video game levels. From the hidden depths of Karazhan to psychedelic space adventures, these secret levels are some of the weirdest, creepiest, and most mysterious in gaming.