When you are at the checkpoint of image 1, go left and use the hookshot to reach the location of the second image. It requires 10 music notes to enter.

At the point of image 1, take a leap of faith pressing the right button to enter the secret area shown on image 2 with the miniboss door. It requires 20 music notes to enter.

When at image 1 location, take the upper route to find the blue chest shown on image 2. There is a hidden path upwards that you can reach with the hookshot tha leads to the door of image 3. 30 music notes are required to access this door.

At the end of the act where you have to guide the lights to open the path, go to the upper right section until you reach the part of the first screenshot. As shown on the image there is a fake ceiling that you can go through using the hookshot. You'll have to use the hookshot a second time. After that follow the path to the left and drop down in the last part to reach the door to the miniboss. It requires 40 music notes.

When you reach the location of the first screenshot use your hookshot to go up. Continue going up until you reach the door of the second screenshot. 50 music notes are required.

As soon as the avalanche section ends you'll be able to drop down to the platform of the first screenshot and then jump to the left to reach the door. It requires 60 music notes to enter.