Fifteen years ago to the day, with some variance depending on where in the world you lived at the time, Thief: The Dark Project, went on sale. It is one of the games that continues to define the possibilities of first-person architecture and also an example of interactive storytelling that has endured over a decade and a half without being fully tapped. Some of the lessons that the team at Looking Glass laid out in their masterpiece has influenced a great deal of gaming. Other parts, like the Thief himself, appear to have gone unnoticed. Here, we remember and celebrate the brilliance of The Dark Project.