Five secret areas are inside the mine.
Secret Area #1
The first secret area is inside the mine. As you continue your journey inside the mine, the Secret Area is on the left side near the first bird portal.
Secret Area #2
From the previous point, go in the right direction and continue the journey in the mine. A little further, you will find the secret area on the right behind the wall. You can reach the Secret Area by rolling.
Secret Area #3
From the previous area, start moving toward the left direction. You will find the Secret Area at the next 2nd bird portal.
Secret Area #4
As you further move inside the mine, you will find the secret area on the right behind the wall. You can reach the Secret Area by rolling.
Secret Area #5:
The next secret area is on the way inside the mine at the third bird portal.
Secret Area #6
After descending from the second elevator, you need to go toward the left. You will find secret area #6
Secret Area #7
Descend from the third elevator and continue your journey on the main path. You can find the next secret area, a level below the main game path (see image).
Secret Area #8
The next secret area is inside one of the trials. Navigate successfully by crossing the giant wheel. You will get the objective to light the first flame. After lighting the flame drop below from the main path to find the secret area.
Secret Area #9
from previous location move toward the right. A little bit ahead you need to climb up to reach the last Secret Area