Every decade has produced its bits of pop-culture nostalgia. The Hula Hoop was big in the 1950s, the Tamagotchi was all the rage in the 1990s, the 1970s saw the Pet Rock, of all things. Perhaps no bit of physical nostalgia -- which is to say, something you can hold in your hands -- to come out of the 1980s is the Rubik's Cube. Though it's forever associated with 1980s nostalgia, the toy, which as of 2009 had sold more than 350 million units worldwide (according to Time), was actually invented back in 1974, according to the Smithsonian. See the full story here