Moaning Myrtle's Bathroom is a girls' lavatory located on the first floor of Hogwarts Castle. It has been out of commission for many years due to the constant presence of the ghost of Myrtle Warren, who haunts it relentlessly. The bathroom is described as gloomy and poorly lit, with most of its light coming from a few sputtering candles and a grimy window. It features a line of chipped stone sinks with tarnished copper taps, a large, cracked, and spotted mirror, and peeling paint on the wooden doors of its cubicles. One of the toilets is permanently out of order. The bathroom's tragic history is central to its identity. On 13 June 1943, a student named Myrtle Warren was hiding in one of the cubicles to cry after being teased by Olive Hornby. While there, she heard a boy's voice speaking a strange language. Upon opening the cubicle door to tell him to leave, she came face-to-face with the Basilisk, which had emerged from the Chamber of Secrets. She died instantly upon looking into its giant yellow eyes. The boy who released the beast was a young Tom Riddle. After her death, Myrtle's ghost returned to haunt the site of her demise, causing so much disruption that the bathroom was eventually abandoned by students and staff, earning it the name “Moaning Myrtle's Bathroom.”
This seemingly unpleasant location plays a pivotal role in several key events throughout the series.