Room of Requirement

The Room of Requirement is a secret room within Hogwarts that only appears when a person is in great need of it. The room then transforms itself into whatever the witch or wizard needs it to be at that moment in time, although there are some limitations. For example, it cannot create food, as that is one of the five Principal Exceptions to Gamp's Law of Elemental Transfiguration. It is believed that the room is Unplottable, as it does not appear on the Marauder's Map, nor do its occupants, although this could simply be because James Potter, Remus Lupin, Sirius Black, and Peter Pettigrew never found the room.

Location
The room is located on the seventh floor of Hogwarts castle and has a hidden entrance opposite the tapestry depicting the attempt of Barnabas the Barmy to teach trolls ballet. The way to open the room is to walk past it three times thinking about what you need, and the door will appear.

"It's a proper hideout, as long as one of us stays in here, they can't get at us, the door won't open. It's all down to Neville. He really gets this room. You've got to ask it for exactly what you need—like, "I don't want any Carrow supporters to be able to get in—and it'll do it for you! You've just got to make sure you close the loopholes! Neville's the man!"

- Seamus explaining the Room of Requirement

It is advised that the users of this room be very specific about what they are looking for, as it has been shown that other people can enter the room and see what the occupant is doing if they know how the room is being used. The Inquisitorial Squad found the hideout of the D.A. in 1996 by knowing that the D.A. was in the room at the time. Neville Longbottom used this knowledge to create his hideout, as he specifically asked that the hideout be made unavailable to those who supported Alecto and Amycus Carrow.

History of use
The first mention of this room was in 1994, when Albus Dumbledore told Igor Karkaroff of his discovery of a room full of chamber pots when he needed to go to the toilet. However, he was unable to find the room again later like many of the those who stumble across the room.

Dumbledore's Army


In 1995, Harry Potter asked Dobby if he knew of a place where Dumbledore's Army could safely meet. Dobby told Harry of what the house-elves called the "Come and Go Room" or "Room of Requirement", which he had used to treat Winky after she had gotten drunk on Butterbeer, as the room filled with antidotes to butterbeer and an elf-sized bed for Winky to sleep off her inebriation. He also said that Argus Filch had found extra cleaning supplies in the room. During the first D.A. meeting, Fred and George Weasley revealed that it had once taken the form of a broom cupboard which they had used to hide from Filch.

Harry and Dumbledore's Army used the room as their headquarters and practice area. Among the items provided by the room for the D.A. were Dark Detectors and shelves of helpful books such as A Compendium of Common Cures, The Dark Arts Outsmarted, Self-Defensive Spellwork, and Jinxes for the Jinxed. They were eventually discovered by the Inquisitorial Squad.

Room of Hidden Things
"I virtually lived in the Room of Hidden Things all last year, I know how to get in."

- Draco Malfoy to Harry Potter

History
Harry used the room in his sixth year to hide the Half-Blood Prince's copy of Advanced Potion Making. He found that many other students had used the room to hide a multitude of other objects, including the Vanishing Cabinet. Inside the cabinet in which he hid the book, Harry found a cage that contained the skeleton of something that had five legs.

Also in Harry's sixth year, Professor Trelawney attempted to use the room to hide her sherry bottles, but Draco Malfoy threw her out. Draco was using the room to repair the Vanishing Cabinet so he could smuggle Death Eaters into the castle via a matching Vanishing Cabinet in Borgin and Burkes. They did in fact use the room to penetrate the castle in 1997.

The Room of Hidden Things became inaccessible whenever the Room of Requirement was used for another purpose. As a result, during the Battle of Hogwarts, when the room was being used to provide passage to Hogsmeade and as a sanctuary, it had to be vacated of all people and "reset" before the Room of Hidden Things could once again be accessed.

Protection
The Room of Hidden Things may have had a special protection that prevented a Summoning Charm being used in it, meaning students had to physically find what it was they were looking for. This was the case when Hermione attempted to summon Rowena Ravenclaw's Diadem, but failed. She, Ron and Harry had to go searching for it instead. However, this protection may have been placed by Voldemort specifically for the diadem, as he took similar precautions for his locket horcrux.

Second Wizarding War
During the 1997–1998 school year, Neville Longbottom and several other students used the room as a hideout to escape the wrath of the new Death Eater professors, the Carrows. The problem was the lack of food, as it was one of the exceptions to Gamp's Law of Elemental Transfiguration. So the hideout adapted by adding an eighth passage into Hogsmeade, connected to the Hog's Head pub, whose owner, Aberforth provided food. Also, this advantage allowed members of the Order of the Phoenix to enter the school to help fight off Lord Voldemort's attack, without setting off the Caterwauling Charm on the village.

Later that same year, during the Battle of Hogwarts, it was used as an evacuation route to move the students away from the dangers that followed. Later, Harry realised that Rowena Ravenclaw's Diadem, one of Voldemort's Horcruxes, was hidden in the Room of Hidden Things, as he has seen it in his sixth year while hiding his Potions book and had even picked it up without realising what it was. As noted above, as long as the room was being used to maintain the passage to Hogwarts, the Room of Hidden Things couldn't be accessed. Harry, Hermione, and Ron cleared the room and accessed the Room of Hidden Things, where they were ambushed by Draco Malfoy, Vincent Crabbe, and Gregory Goyle. Crabbe let loose cursed fire that destroyed the Horcrux and many other objects, killing himself in the process.

Items hidden inside
Harry Potter saw many things that other students had hidden in the room, including:
 * Broken and damaged furniture, perhaps hidden to hide mishandled magic
 * Thousands and thousands of books, probably banned, graffitied, or stolen
 * Flying catapults
 * Fanged Frisbees
 * Chipped bottles of congealed potions,
 * Corked bottles whose contents still shimmered evilly
 * What looked like dragon eggshells
 * Several rusting swords
 * A heavy, bloodstained axe
 * An enormous stuffed troll
 * The broken Vanishing Cabinet that Graham Montague had gotten lost in during the previous school year
 * Hats, jewels, and cloaks
 * A cage with a quintaped skeleton
 * The lost diadem of Ravenclaw, made into a Horcrux
 * The Half-Blood Prince's copy of Advanced Potion-Making
 * A chipped old bust of an ugly warlock
 * A record turntable that "skipped".

Behind the scenes

 * In the fifth film, Neville Longbottom found the Room of Requirement, since Dobby was cut from the film.
 * In the sixth film, Harry and Ginny had their first kiss in the Room of Hidden Things, instead of the Gryffindor common room.
 * In the eighth film, Gregory Goyle casts the Fiendfyre curse in the Room of Hidden Things, destroying the diadem and killing himself in the process, since Vincent Crabbe was cut from the two-part film. Also, Blaise Zabini is present at the fight.
 * In the Harry Potter and the Half-Blood Prince video game, the Room of Requirement can be found on the sixth floor, even though in one of the scenes in the game Harry says the room is on the seventh floor. In the fifth game, fifth film, and all the books, the room is on the seventh floor. Presumably this is because the first floor in Europe is called the second floor in the USA.
 * The Room of Requirement is the main location of the Nintendo DS version of Lego Harry Potter: Years 1-4, despite being introduced in Harry Potter and the Order of the Phoenix.
 * In the Harry Potter and the Philosopher's Stone video game, the Room of Requirement is possibly mentioned by Albus Dumbledore, who was walking around the castle and found a room full of Chocolate Frogs. On another day, however, the room was filled with Fire Crabs.
 * In Harry Potter and the Deathly Hallows: Part 2, in the Room of Hidden Things can been seen some chess piece from the giant Wizard's Chess Set of Harry Potter and the Philosopher's Stone.

Appearances

 * Harry Potter and the Philosopher's Stone (video game)
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2
 * Lego Harry Potter: Years 1-4