Get all 8 musical coins in every level in the game before you open time atack to get a 4th golf minigame course, which can be played between N world and W world once all 7 crayons are aquired.
You will find a crayon in the gray chest of Above the Clouds, the green chest of The Desert Ruins, the red chests of the Warped Void, Beneath the Waves, the Big Bridge, and the Vast Plain, and finally, the blue chest of the Pool of Rain. You'll unlock the building between the north and west after getting the crayons.
Get all the treasure in each level to play the Time Attack Mode