This page of the Resident Evil Village guide provides a detailed description of the 5 bells puzzle from the Atelier room in Dimitrescu Castle. The following tutorial will tell you where to find all 5 bells and how to activate each one of them correctly.
Place of solving the bell puzzle
You can solve this puzzle in the Atelier room on floor 2F of the castle. You can reach this room for the first time shortly after defeating the last third vampire in the Library.
There's a Dimitrescu's Portrait in the room. In addition, there is a note attached to the smaller painting with a hint on how to solve the puzzle.
Finding the five bells
Your task is to find 5 bells in Atelier room that can be shot at. It is best to use a pistol to solve the puzzle and thus not waste ammunition for better weapons. You can shoot the bells in any order - the order below is just an example.
The first bell is on the round table next to the portrait.
The second bell is quite problematic. It has been attached to a pendulum that operates behind a wall filled with holes. You must wait until the bell is briefly exposed behind one of the openings (see image above) and then quickly fire a shot. If you miss, you can of course repeat the attack.
The third bell is more difficult to spot because of its small size. It was placed on a large piece of furniture, in front of a painting.
The fourth bell forces you to use a small staircase in the room. After you go upstairs, shoot the chandelier near the ceiling to make it swing. It will expose the bell and you must shoot again at the perfect moment.
You can shoot at the fifth bell from the same place you hit the fourth bell. Inspect the windows near the ceiling. Look through them and you'll see a bell located outside. Aim at it and make the bullet break the shutter while flying to the target.
By "lighting" all 5 bells, you will unlock the passage behind the big painting.