The Door That Does Not Open

"There was a door in the North Castle called 'The Door That Does Not Open'."

The Door That Does Not Open is an object from Zelda II: The Adventure of Link. Located within the North Castle, it leads to the room where Princess Zelda sleeps. The only people who know how to open the door are the descendants of the Impa family who served the Great King of Hyrule. Prior to the game's events, Impa opens the door by touching it with Link's left hand, which bears the Mark of a Hero. Inside, Link sees Princess Zelda and learns that she was placed into a deep slumber by a Magician.