A man in a gold mask walks around the mansion. The first time you see him, you unlock this achievement.
One way to unlock it is to wait in the room with a narrow walkway and a massive window, just North of where you first enter the main mansion. He eventually walks across the walkway.
The simplest way to unlock this is to play through the story. If you've not already met him, you'll unlock this automatically a little under halfway through, after gaining the power to shatter glass.