It does an odd calculation involving the player's position on the map. It subtracts the Y coordinate from the X, takes the absolute value, and then does modulo 4. Depending on the end result, it will send you to just outside the tunnel in the Highway, the moonlit balcony that used to be part of the Dark Museum but has been moved around so many fucking times I have no idea anymore, the western half of the Day & Night towers, or the mermaid lake in Jigsaw Puzzle World.