All you have to do is get 150 stars and use the cannon and blast to the top. You can also check You Tube for a glitch and a secret to get to the top of the castle without 150 stars.
Also, there are 3 more ways.
1. You can be Luigi and back flip onto the little cliff on the waterfall on your right. Once on there, turn your camera view, and keep pressing B till you get up on top. Difficulty:1/5
*This is a glitch in the original Nintendo 64 version*
2. Be Mario and go all the way to your left and on a little hill triple jump, and wall kick up the wall. Difficulty:4/5
3. Be Yoshi, and go to the little cliff on the right, and keep pressing B till you are high enough to the castle. Hope that helps. Difficulty:1/5
*This is a glitch in the original Nintendo 64 version*
4.Be Wario and keep on ducking and sliding up the hill at the right until you can't fall, then run fast to the castle. Difficulty:5/5 Note: This is really hard to do, you have to practice a lot!
on top of the castle
fly
By canon or moon jump with action replay ds
You can't.
get all the stars to unlock the cannon
do you mean a winged cap. if so, it is in levels and on top of the castle
On top of the hill. After Princess Peach sends Mario the same note as the original Super Mario 64. :)
You use the moon jump cheat.
farty
When you get the last Power Star it will open. There are 120 in the original and 150 in the DS remake.
To get on the castle roof of the castle
You go to the top of the castle and defeat Bowser. After you have defeated Bowser you will have completed the game. If you did that and you won. CONGRATULATIONS