Change your character to Luigi and go outside near the waterfall. If you are in the correct place, which is near the fence, turn your back to the little piece of land across the water. Do a backflip (R + B) and you will start twirling. Try to twirl to the little piece of land (not the steep side). Turn your back to the steep part of the hill and change the camera position so the it is showing your back. Jump and scuttle while holding Down and you will get up the hill a short distance. Then, just as you touch the ground press B(2) and hold it while pressing Down. Keep doing this until you get to flat surface at the top. Jump onto the red roof. It is steep, but it has a lot friction so that you will not slide down. There will be a rabbit, a "?" box, and three 1-Ups here.
Change your character to Mario, go outside, then keep going to the left. You will see that there is a corner formed by the castle. Do a triple jump, then wall jump kick on the wall. Then use another wall jump kick on the other wall and continue until you reach the top.
Change your character to Yoshi. Go near the waterfall, but not in it. Turn your back to the steep hill. Press B, then when you touch the ground press B (2) (Luigi's technique). Keep doing this until you are high up the hill. Try to slide down onto the little piece of land. Do the same thing up the hill and you will be there.