The blast shield end of the Apollo 11 command module, Columbia, which carried home the first men to set foot on the moon. They trucked this around America on a flatbed trailer in the months after it landed. I saw it in Des Moines as a kid and managed to pry a fleck of paint off it with a thumbnail, put it in my pocket, and promptly lost it. That's why they cover it with plastic, so numbskulls like me can't tear it up any more.