The cache in the castle is one of many side quests that you can perform in the Hogwarts Heritage to get additional awards, as well as the opportunity to explore many secrets of Hogwarts.
You can start a side quest in the astronomical tower after the end of the medallion, the main plot quest.
Talk to Arthur Plasma near the spell class to find out about the treasure map that he wants to decipher.
You will receive a treasure map on which there is nothing but three different attractions: a skeleton, a fountain and paintings.
These are your only tips where the treasure lies.

Passage cache in the castle

As soon as you get a card from Arthur, it’s time to go in search of treasures.

Find the first landmark

On your map you will see a drawing of a skeleton of a rhino, which is your first landmark.
To get to this attraction, climb the stairs, go down three floors and turn left until you reach the central staircase.
This staircase will lead you to the skeleton of the rhino located between the two balls.
Go to the skeleton, your character recognizes this, and a new quest marker will appear.

Find the second landmark

The second attraction mentioned on your map is the Fountain of the Dragon Statue.
You can visit the Preobrazhensky yard manually or using a system for transporting flying powders.
If you decide to go manually, you need to climb the stairs near the skeleton of the rhino and go down until you see two huge doors leading to the exit from the protection tower from the dark arts.
Once in the courtyard of the transformation, you can see the fountain of the statue of the dragon, and a new quest marker will appear for the third landmark.

Find the third landmark

The third and last landmarks in this quest are a picture.
To find this picture, you need to climb the stairs right behind the fountain in the Preobrazhensky court.
Go up the stairs, and you will have a large picture with the image of a house in the snow.

look for a treasure

As soon as you found all the landmarks, you still have to look for a hidden chest with treasures.
Standing in front of the third landmark, say action on the upper handle of the picture.
This will open a secret chest with treasures hidden behind a large picture.
As soon as you found a chest, you can look for your treasure in it.
Open the chest, and you will receive a genuine uniform of a historian, a collectible mantle that you can use to change the appearance of your character.

Hogwarts

Return to Arthur

Now return to Arthur and talk to him.
He will tell you that he found money using his card, and this will complete the side quest.
Together with the mantle, you will also get 180 experience points.