WeisGuy9's guide is solid but a couple of notes may help.
You control the dwarf and the satyr for this level. controlling the dwarf (Trumpkin) can help you grind toward "Trumpkin's Delight" achievement, but there are other levels for that; you're best left using the satyr for his staff melee (helps to clear the area when you're being mobbed) and for his archery (essential for taking down the chandellier.
Once on the second level/balcony, you'll notice archers firing at you from the far side; use the satyr to kill them if you'd like, but you only need to shoot the chandellier down to advance the story and move into the next cutscene.
After you clear the final room of Telmarines, DO NOT OPEN THE CHEST. Not immediately. Turn around and run toward the camera to the far end of the room to find a chest and retrieve a bonus. Also, as stated above, search behind the thrones for an additional (non-chest) bonus.
OK, now you can open the chest with Susan's horn in it.