Go into the castle and go in the door with a blank star on it (to your left). collect the seven stars on that level. then go into the door that displays the star with the number 1 on it (to your right, Whomps' fortress). collect three stars. you should have a total of ten stars. go to the main entrance and on the middle of the floor there is a sun. stand on the sun and press up C and press and hold down so you are looking directly into the beam of light shining down from the roof. you will be taken to the flying cap bonus. fly down to the platform directly beneath you by holding up on the control pad. there will be a red switch with an exclamation mark on it. step on that switch and you will be able to use the flying cap.