A Large Keyhole (あやしいトビラ, Ayashii Tobira, lit. Suspicious Door) is an event in Tomba!.
Find a large key to unlock the door.
The Large Key is needed in order to open one of those doors and clear the event. It can be obtained by clearing the Painting of a Big Key? event found in the Haunted Mansion. Approach one of the mentioned doors with the Large Key to clear the event.