There are many rooms at Hogwarts that require a password for you to enter. The following is a list that have been used:
Chamber of Secrets
"Open Up" - Parseltongue
Gryffindor Common Room
Fairy Lights/Lairy Fights
Tickle the huge green pear in the picture of a giant fruit bowl.
Professor Dumbledore's Office
Room of Requirement
Walk past the tapestry of Barnabas the Barmy three times while concentrating hard on what you need.
Secret Passage to Hogsmeade
Dissendium - use your wand to tap the hump on the humpbacked, one-eyed witch on the third floor.
Slytherin Common Room
Ravenclaw Common Room
Those who wish to enter must correctly answer a difficult question.
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