Purge and Dowse, Ltd. is the secret, Muggle-proof entrance to St. Mungo's Hospital for Magical Maladies and Injuries, located in a busy area of London. To any non-magical person, it appears to be a shabby, old-fashioned department store named “Purge and Dowse, Ltd.,” which has long been closed for business. The building is made of red brick, and its display windows are described as grubby. The main display window contains several lopsided mannequins, some missing limbs or heads, dressed in outdated wizarding robes of clashing colors like green and blue. The sign above the door, bearing the company's name in gold letters, is the only well-maintained feature. The entire facade is enchanted to be unnoticeable to Muggles, who will walk past without giving it a second glance. To enter St. Mungo's, a wizard or witch must stand close to the display window and speak to the particularly unattractive female mannequin positioned at the front. The visitor must state their business clearly. For example, Molly Weasley whispers, “We're here to see Arthur Weasley.” Upon receiving a valid reason for entry, the mannequin gives a small, stiff nod and beckons the visitor forward with its jointed finger. The visitor can then walk directly through the glass of the window, which ripples like water, and emerge into the reception area of the hospital.
The location's primary appearance is in Harry Potter and the Order of the Phoenix. It serves as the entryway for all visitors to St. Mungo's.
Purge and Dowse, Ltd. is merely a facade. It has no accessible interior of its own. The only significant feature is the enchanted display window, which acts as a magical portal. Passing through it leads directly into the reception area of St. Mungo's Hospital for Magical Maladies and Injuries.