The First-floor Girls' Lavatory, more commonly known as Myrtle's Bathroom is situated on the first floor of Hogwarts Castle, just above the Great Hall.
It has been out of order ever since a student named Myrtle was killedthere. Myrtle has haunted the bathroom ever since the Ministry of Magic stopped her from haunting Olive Hornby who had been teasing Myrtle just before her death, leading it to be a place most students do not want to enter.
Myrtle says Hi !