“Blood Bulls” is an optional mystery puzzle that you can find in Indiana Jones and the Great Circle during “The mummy of the stolen cat.” It's very easy to miss, but you can find it in the Castel Sant'Angelo on the way to meet Father Antonio.
Our Indiana Jones and the Great Circle The guide will show you where to find the secret passage and how to solve the “Blood Bulls” puzzle.
How to start 'Blood Bulls'
On your way to meet Father Antonio on the steps of the town, you will have to cross the Castel Sant'Angelo strength. After some sneaking, beating up fascists, and some climbing, you'll complete the objective of “get to the top of the castello” and start a new one, “get to Passetto di Borgo.”
Shortly after, you will find yourself in the Angel Courtyard. After dealing with the patrolling Blackshirts, head to the first door on the right.
Inside, you can Russo's note on the desk. Mention “the passage” next to a fireplace and he will add the The mystery of 'Blood Bulls' to your diary.
Solution to the 'Blood Bulls' puzzle
From where you picked up the note (with your back to the fireplace), head north and through the hallway on the right side of the room.
Head straight into the next room (there's nothing to find there) and you'll be faced with the puzzle. Look at the desk on the right for some clues.
You will find a Map of the Angel Courtyard (spoiler: it tells you exactly where you are standing), and a red bulls card (which is your clue to solve the puzzle) along with some lyre.
From that desk, look to your right to find the “Blood Bulls” puzzle. The two bull paintings on the wall are the ones you have to interact with. The Red Bulls card shows the two red bulls facing each other, so interact with each painting and rotate them until the red bulls are on top.
Enter the secret passage to find César Borgia's letter. Go up the stairs and flip the switch on the wall to open a door and earn your 100 adventure points.
There is a chest in front of you with more lyres inside. To the left, you will find another switch that opens another door that returns you to the main path.