Answer
The answer is as follows. 
Katrielle and the Millionaires' Conspiracy walkthrough
Puzzle Location: Cellar (The mirror)
Get your light to shine on the treasure at the bottom of the lake.
Beneath the water lie mysterious crystals that reflect light just like mirrors.
If you touch one of these crystals, it more than doubles in size, and can change the direction in which your light travels.
They say something happens if the treasure is illuminated...
There are several ways to make your light reach the treasure.
Here, we'll look at a solution that involves making five crystals bigger.
When the light reaches the treasure, the second crystal that the light hits around the middle are will be bigger.
Continuing on from hint one...
The third crystal the light hits at the bottom-right should be big.
Continuing on from hint two...
The fifth crystal the light hits at the top-left should be big.
Continuing on from hint three...
The sixth crystal the light hits at the top-right should be big.
The treasure isn't far now.
The answer is as follows.