The entrance to the cathedral is located in the city center  from the north side. 
Start climbing from the white bench.  Climbs to get to the platform. 
Turn right - you will see the way.  Jump from the beam on chandeliers. 
Standing on the chandeliers rotate backwards - you have to go back now.  Then turn left towards the ladder located on the wall. 
Get on the shelf with stained glass and rotate - now jump on the beam and swing.  You will land on the next beam - jump on the next platform near the second stained glass window. 
You will have to jump on the railing again.  A little further swing to hit the chandelier. 
From chandeliers get to a wooden platform located in the middle.  Birds on the edge will "tell" you where to go - you have to go back a bit. Now you can go on the shelf near the window. 
Climb to a higher part of the shelf.  Before you will swing turn your character to land on the chandelier. 
Climb to a higher part of the shelf.  Go deeper into the church and jump off on the platform with the ladder. 
Jump on the railing and turn right. Jump on the huge music instrument.  Then to the railing and on the chandelier.  Using the next beam to the second instrument.
Return to the middle railing and go further until you will see the platform hanging from the ceiling.  Jump on it them and then on the beam where you will be able to reach the handles. 
Above, head towards the shining wing of the church.  Here, climb using windows and get to the higher level. 
Go back to the center and turn left - jump on the hanging platform and come closer to pigeons.  Get to the second lighted aisle and climb using windows. 
Go to the left and jump to the balcony.  Then jump on the platform that is hanging over the abyss and then get to the second balcony. 
At the end of the second balcony there is a ladder leading to the top.  Jump around the room using beams Sticking out from the wall. On the other side climb using some missing bricks. 
At the top make a big jump on the central platform.  Use two ladders, take all treasures  and go using the window.