Getting the achievement is pretty simple, once you know where to look. First, load up the Winter Wasteland level and as soon as the race starts, immediately turn around and start racing back along the right edge of the course. Keep going until you see this house:


Go just past it and turn around so it looks something like this:


See that tree? You're going to want to run into the wall next to that until you spot a little hidden Santa:


Once it's visible, the achievement should pop up.