Purge and Dowse, Ltd is a department store located in London. While outwardly appearing to be a red brick Muggle clothing store under renovation, the dilapidated building actually disguises the entrance to St Mungo's Hospital for Magical Maladies and Injuries.
Entrance to St Mungo's
Entrance to St Mungo's is achieved by speaking to a mannequin in one of the shop windows and stating your reason for wishing entry. Once the mannequin nods its assent, the people who wish entry may walk through the window and into the reception area of St Mungo's. The theory behind using this building for the entrance to St Mungo's was that injured witches and wizards could simply blend with the Muggle crowd on their way to the hospital.
According to Muggle shoppers, the store is always "under renovation" and is never open.
- Harry Potter and the Order of the Phoenix (First appearance)