In level 15 Rainbow Ride, ride the carpet all the way up to the Floating Mansion. Walk out of it and stand in the grey area in between the Mansion Entance and the Wooden Platform. you will be teleported to the top of the Red Coin Maze or vice versa. Be careful, on top of the Red Coin Maze, there is a 1-Up Mushroom but you can also be blown off by the wind.