Common Room

• Type: Lounge, study, and social hub
• Location: Within Hogwarts Castle, one for each of the four Houses
• Owner/Residents: Students of the corresponding Hogwarts House
• Key Features: Guarded entrance unique to each House, comfortable seating (typically armchairs), a fireplace, and a notice board for announcements.

A Common Room is a dedicated area within Hogwarts Castle for the students of a single Hogwarts House. It functions as a central hub where students can relax, socialize, study, and hold house celebrations. Each common room is located in a different part of the castle and is furnished according to the themes and colours of its respective House. Access is restricted to members of that House (and its faculty Head) and is protected by a magical guard, such as a password-requiring portrait or a riddle-asking door knocker, to prevent entry by students from other Houses. The common rooms are connected to the dormitories for their students.

Located in Gryffindor Tower on the seventh floor, the entrance to the Gryffindor common room is concealed behind a portrait of the Fat Lady. To enter, one must provide the correct, frequently-changing password. The room itself is a cozy, circular space decorated in scarlet and gold. It is filled with squashy armchairs, tables, and a large fireplace that is often used for communication via the Floo Network. A notice board in the room displays important announcements, student-made advertisements, and official school decrees.

The Slytherin common room is situated in the Dungeons of Hogwarts Castle, behind a stretch of bare, damp stone wall. A password is required to make the entrance appear. The room is a long, low, dungeon-like chamber lying beneath the Black Lake, which gives the space a dim, greenish glow. The decor is austere and grand, featuring elaborately carved stone chairs, tapestries depicting the deeds of famous Slytherins, and numerous skulls as part of the decoration. Its atmosphere is notably colder than the other common rooms.

The Ravenclaw common room is located in Ravenclaw Tower on the west side of the castle. Its entrance is a door without a doorknob, featuring a bronze, eagle-shaped knocker. Instead of a password, the knocker poses a philosophical riddle that one must answer correctly to gain entry. The room is a wide, airy, circular space with graceful arched windows offering spectacular views of the castle grounds. Decorated in blue and bronze, it has a domed ceiling painted with stars and features a white marble statue of its founder, Rowena Ravenclaw. The room is filled with tables, chairs, and bookcases, reflecting the House's emphasis on learning and wisdom.

The entrance to the Hufflepuff common room is located in the same corridor as the Hogwarts Kitchens. It is concealed within a pile of large barrels. To enter, one must tap the barrel two from the bottom, in the middle of the second row, in the rhythm of 'Helga Hufflepuff'. Tapping the wrong barrel or the wrong rhythm will cause one of the other lids to burst open and douse the intruder in vinegar (Pottermore). The common room itself is a cozy, round, low-ceilinged room that is perpetually sunny. It is decorated in cheerful yellow and black, with burnished copper details and many plants. The circular doors lead to the dormitories, and the overall atmosphere is described as earthy and welcoming (Pottermore).

The common rooms, particularly the Gryffindor one, serve as a primary setting for much of the series' exposition, planning, and character interaction.

• Plot Development: Harry Potter, Ron Weasley, and Hermione Granger use the common room to discuss their plans and decipher clues, from the Philosopher's Stone to the plots of Lord Voldemort.
• Social Hub: The room is the site of numerous celebrations, such as winning the Quidditch Cup or the House Cup. It is also where key relationship moments occur, such as Harry and Ginny's first kiss.
• Conflict and Information: It serves as a stage for conflicts, like the argument between Harry and Seamus Finnigan about Voldemort's return, and as an information center via the notice board and conversations.
• Infiltration: The Slytherin common room is notably infiltrated by Harry and Ron Weasley using Polyjuice Potion to interrogate Draco Malfoy.
• Key Events: Sirius Black twice used the Gryffindor fireplace to communicate with Harry. The Ravenclaw common room was the site of a critical confrontation between Harry, Luna Lovegood, Minerva McGonagall, and the Carrows just before the Battle of Hogwarts.

• In the books, Harry only ever enters the Gryffindor, Slytherin, and Ravenclaw common rooms. The appearance and entrance mechanism for the Hufflepuff common room were detailed by J.K. Rowling on the Pottermore website.
• The film adaptations created highly detailed and iconic sets for the Gryffindor and Slytherin common rooms. The Gryffindor set is particularly memorable for its warmth and lived-in feel, establishing a strong visual identity for the House (film).
• In Harry Potter and the Chamber of Secrets (video game), the player can find a witch's hat in the Slytherin common room that belonged to Salazar Slytherin's daughter (video game).
• The Ravenclaw common room's riddle-based security makes it the only one that a member of another house could theoretically enter, provided they are clever enough.