Number Twelve, Grimmauld Place
Appearance
Number Twelve, Grimmauld Place, London is a fictitious place in the Harry Potter books and is specifically mentioned in the fifth book.
It is the headquarters of the Order of the Phoenix and was originally Sirius Black's family home. It is a very strange place which includes a hysterical portrait of Black's mother who has a deep seeded hatred for non-Purebloods. There is also a house-elf named Kreacher who seconds to this opinion.
"Grimmauld Place" is a pun on "grim old place."