The First-Floor Girls' Bathroom

• Type: Washroom
• Location: Hogwarts Castle, Scotland (located on the first floor, though also referred to as being on the second floor)
• Owner/Residents: Hogwarts School of Witchcraft and Wizardry; haunted by the ghost of Moaning Myrtle
• Key Features: Mostly out of order; prone to flooding; conceals the entrance to the Chamber of Secrets

The girls' bathroom on the first floor of Hogwarts Castle is a gloomy and disused lavatory, primarily known for being the permanent haunting ground of the ghost Moaning Myrtle. Due to Myrtle's constant wailing, sobbing, and habit of flooding the room, most students avoid it, leaving it in a state of disrepair. The bathroom is described as having peeling paint, cracked and spotted mirrors, and a row of chipped stone sinks with tarnished copper taps. Its history is intrinsically linked to the Chamber of Secrets. On 13 June 1943, a student named Myrtle Warren was hiding in one of the bathroom's stalls to cry after being teased by Olive Hornby. It was then that Tom Riddle, the Heir of Slytherin, opened the Chamber of Secrets from within the bathroom. Myrtle, hearing a boy's voice, opened the stall door to tell him to leave and was met with the fatal gaze of the Basilisk, which killed her instantly. Her body was discovered there hours later. After her death, her ghost returned to haunt the site of her demise. One of the sinks in this bathroom serves as the concealed entrance to the Chamber of Secrets. This particular tap has a small snake scratched onto its side and has never been functional.

This bathroom is a significant location in several key events throughout the series. In Harry Potter and the Chamber of Secrets, the bathroom's disused state makes it the perfect hidden location for Hermione Granger to brew the complex and forbidden Polyjuice Potion. Harry Potter, Ron Weasley, and Hermione use it as their base of operations while investigating the attacks on students. It is here that Harry, prompted by a detail from Tom Riddle's Diary, discovers that he can open the entrance to the Chamber of Secrets by speaking Parseltongue to the snake-engraved tap. Later, Moaning Myrtle provides Harry and Ron with the final clue they need to identify the Chamber's monster, explaining that she died after seeing a pair of large yellow eyes in the pipes. In Harry Potter and the Half-Blood Prince, the bathroom serves as a private refuge for Draco Malfoy, who is struggling under the weight of the task given to him by Lord Voldemort. He is often found there crying and confiding in Moaning Myrtle. Harry follows Draco to this bathroom and confronts him, leading to a fierce duel. The confrontation culminates in Harry casting the Sectumsempra curse, a spell he learned from the Half-Blood Prince's Advanced Potion-Making book, which severely injures Malfoy. Severus Snape arrives moments later to heal Draco's wounds.

• The Stalls: Cubicles with wooden doors where students could find privacy. Myrtle Warren died in one, and Hermione Granger later used one to set up a cauldron for the Polyjuice Potion.
• The Sinks: A row of chipped stone sinks. Most are functional, though the plumbing is poor and often contributes to the flooding caused by Moaning Myrtle.
• Entrance to the Chamber of Secrets: One specific sink acts as the secret entrance. Speaking the Parseltongue command “Open” to the snake carving on the tap causes the sink and the wall behind it to retract, revealing a large, dark pipe leading down into the depths of the castle.

• There is a notable continuity error in the books regarding the bathroom's location. In Harry Potter and the Chamber of Secrets, it is explicitly stated to be on the first floor. However, in Harry Potter and the Half-Blood Prince, Harry finds Malfoy in the bathroom haunted by Moaning Myrtle on the second floor. It is widely assumed this refers to the same bathroom and that the discrepancy is a minor error.
• In the film adaptation of Harry Potter and the Chamber of Secrets, the entrance to the Chamber is depicted as a large, circular arrangement of sinks in the center of the room. The snake-engraved tap on one sink acts as a key, causing the entire structure to retract into the floor and reveal the entrance pipe (film).