I have defeated the three bosses but it does not unlock the door. help?
After you defeat each boss, there is a riddle / puzzle that you must solve in each room, and you get a message something like "a door is unlocked".
Did you solve the riddle in each of the three rooms?
Watch for the yellow banners hanging on the walls to light up. They will show you a clue as to what you have to do. Whatever items you see on the banners, you must use to light up the things in that room.