Spoiler
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Go to the room where there are 4 signs on the floor,you need to turn the signs in a good order,and when you do,a door will open and you'll get in a room where there are 2 mages you kill them and you proceed to the other rooms
You'll find a door,than go downstairs,kill the Golems,and insert the Demon heart in the "machine".
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Don't mess with the Lich