Sorry for the delay, I needed to take some printts for demonstration because it's not obvious. Firstly there is an invisible lever next to the fake ladder, inside the red circle, this releases a 2 ladder near the blocks where the arrow is pointed. You will unlock the second dark area, there will also be a hidden lever. This will remove a line of blocks leading to the last room. The lever is somewhere inside the red circle, it's small. In the last one, so far, everything I've found is a small platform, I've represented it with a red line. It's hard to get under it because of this damn enemy that spans endlessly. If he touches you, you fall and return to the first room.