Keyhole

Keyholes are secret level passages in the game Super Mario World. Every level in the game that is represented by a red dot on the map has a secret exit; in most of these levels the secret exits are keyholes. To reach the secret levels, Mario or Luigi must find a key and bring it to the keyhole. If Mario or Luigi is riding Yoshi, Yoshi must hold the key in his mouth and simply walk to the keyhole. When the keyhole is activated by the key, the keyhole increases in size. Mario or Luigi will then go inside the keyhole, along with Yoshi, if the player is riding him.

A keyhole is seen in the episode "Mama Luigi" in the Super Mario World television series, where Baby Yoshi spat out the key he held in his mouth at the keyhole, which allowed Mario, Luigi and Baby Yoshi to rescue Princess Toadstool and return to Dome City.