Location from harry-potter-order-of-the-phoenix by
The ancestral London townhouse of the Black family -- dark, hostile, and the secret headquarters of the Order of the Phoenix. Sirius's prison. Kreacher's domain. A house that hates most of the people living in it.
Grimmauld Place is the Order's headquarters and Sirius's cage. The Fidelius Charm keeps it hidden -- Dumbledore is Secret-Keeper -- and the house fights the Order's presence at every turn. The curtains over Mrs. Black's portrait can't be removed. Kreacher mutters insults and steals silverware. Dark artifacts lurk in every drawer. A boggart lives in the writing desk upstairs and takes the form of each person's worst fear. Harry arrives here after the Dementor attack and the disciplinary hearing, angry and isolated, to find his friends have been together all summer without him. The house is where Molly's boggart shows her family dead. Where Sirius drinks and broods. Where Extendable Ears let the children eavesdrop on Order meetings. Where everyone who believes Voldemort has returned gathers to plan, argue, and wait for a war the Ministry says isn't coming.
A tall, grim townhouse that materializes between numbers 11 and 13 when you know the secret. Inside: peeling wallpaper, gas lamps, a troll-leg umbrella stand that Tonks trips over every time, mounted house-elf heads on the staircase wall, and the permanently stuck portrait of Walburga Black who screams 'BLOOD TRAITORS! FILTH! SCUM!' whenever the curtains are disturbed. The kitchen in the basement is the only warm room, where Order meetings take place around a long table.
Also known as: Grimmauld Place, 12 Grimmauld Place, Number Twelve, Black family house, Order headquarters