Location from Harry Potter by J.K. Rowling
A hidden enchanted room on the seventh floor of Hogwarts that manifests as whatever the seeker most needs, from a training space to a bathroom to a vast warehouse of centuries of hidden objects.
The Room of Requirement is Hogwarts at its most sentient and obliging. Walk past the blank wall three times while concentrating on what you need, and a door appears. Need a place to hide? Done. Need a bathroom? There's one with a particularly fine selection of chamber pots. Need somewhere to train an illegal student defense group while a toad-faced Ministry spy runs the school? The room provides cushions, books, and a whistle. The Room of Hidden Things is its most famous configuration — a vast cathedral of discarded objects where Ravenclaw's lost diadem sat unnoticed for a thousand years, where Malfoy spent sixth year repairing a Vanishing Cabinet, and where Fiendfyre eventually consumed it all. The room cannot create food or extend beyond the castle walls, but within those limits it is essentially wish fulfillment in architectural form.
The room has no fixed form — it becomes what you need. For Dumbledore's Army it was a spacious practice hall with cushioned floors, Dark-detector mirrors, and shelves of Defense books. As the Room of Hidden Things it was a city-sized labyrinth of towering junk — broken furniture, confiscated items, old textbooks, cages, bottles, hats, jewels, weapons — centuries of Hogwarts secrets piled cathedral-high. The entrance appears as a door in a blank stretch of wall on the seventh floor, opposite the tapestry of Barnabas the Barmy.
Also known as: the Room of Requirement, Room of Requirement, the Come and Go Room, Room of Hidden Things