First you will have to fight against a boss that brings the queen.
It’s a simple boss I think, attack him with magic or physical attacks, both are good.
After passing a couple of enemies you will cross a door and you will find 3 eyes.
These eyes block you from using magic so you can only attack with physical attacks.
The first or recommended thing is to attack the middle eye because it is the only one that attacks you.
After destroying that eye you have to attack the others, either of the 2. The thing is that one of those eyes can run away if you take too long to destroy it.
If one of the eyes disappears and you only kill 2/3
you will get 500 XP and 100 PT.
Now if you kill all 3 eyes before one runs away, you will get 1000 XP and 200 PT. The good thing about this is that you can go back through the back door and go back through that door and the 3 eyes will be there again, you can do it as many times as you want.
Thanks to suzaku for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.