What’s hidden behing your wallpaper? A painting masterpiece?

Looking at a wall with a daub painted on it, digging a little, to find a wonderful wall art by a handful of extraordinary artists, this doesn’t happen every day. I’m sure you won’t try to remove your grandmother’s flowered wallpaper hoping to find a Picasso. But who knows what you could discover? A message from a time traveler? A sacred text which would change our perspective on the world’s history?