Grimmauld Place in fanfics often becomes this wild canvas for reinvention once Harry gets ownership. Some writers turn it into a cozy, magical haven where he hosts Dumbledore's Army meetings with homemade treacle tart and charmed fireplaces. Others go darker—imagine cursed artifacts left by Sirius' family suddenly reacting to Harry's presence, whispering secrets or even trying to possess him. I once read a fic where Kreacher, of all people, becomes weirdly devoted after Harry gifts him a handmade tea cozy, and they team up to purge the house of dark magic together. It's fascinating how one location can swing from 'found family headquarters' to 'haunted horror show' depending on the writer's vibe.
Then there's the trope where Harry discovers hidden rooms—like a secret potions lab or a library with Black family grimoires. One memorable story had him finding Regulus' old journals, which sent him on a whole side quest about Horcruxes years early. The house almost becomes a character itself, shaping Harry's growth. Bonus points if authors describe the portrait of Mrs. Black screaming insults until Harry, fed up, repurposes her frame as a dartboard.