The secret door Kili, Fili and Bilbo find the secret door on the Lonely mountain. When the setting sunlight touched the door it revealed the keyhole. They opened the door into a dark tunnel.
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Inside information Bilbo stole a gold cup from Smaug which made the dragon angry. While Bilbo talks and riddles with him he notices a bare spot on Smaug's chest. Smaug flies off to attack Laketown thinking Bilbo had help from them.