At the very end of Greatest Hits, there is an odd upside-down room that can be found, with a car and some crates located in it.
At the very end of the track, at the finish line, slowly drive past the finish point. You will be picked up by the wind and carried upwards. If everything goes well, you should be elevated into an upside-down room with an inverted camera view, and you'll see a car and some crates resting on the ceiling (now the floor).
As of yet, there is no known meaning for the car or the crates, or for the room being upside down at all. For the moment, the room is noted as simply being a silly little easter egg.
This section is reserved for Confirmation/comments about this investigation. Investigations will remain open until advised by Redlynx that the final solution for each secret is found.