"Now you will see your birthday present, and I hope you like it," said the Doctor, drawing a key on a blue silk ribbon from his pocket. The key was a rod of steel having a fabulously ornate handle at one end, and at the other, a sort of three-dimensional maze carved into a steel cube. He inserted this into a square hole in the door-lock, wiggled it to and fro to make it one with the mechanism concealed inside, then turned it. Before opening the doors, he removed the key from the lock and hung it on its blue ribbon around the Princess’s neck. "Since you cannot carry your present with you, I hope you’ll carry this key as a token. May you never be locked out again."