Location from harry-potter-half-blood-prince by
This year: Draco's secret workshop, where he repairs the Vanishing Cabinet that lets Death Eaters into Hogwarts.
The Room transforms into the Room of Hidden Things for Draco — a vast cathedral-sized space filled with centuries of confiscated items, broken furniture, and hidden secrets. The Vanishing Cabinet sits among the junk. Draco spends months repairing it, and when he succeeds, Death Eaters pour through its twin in Borgin and Burkes.
Whatever you need it to be. For Draco: a cluttered room of hidden things, piled with centuries of Hogwarts detritus, containing the broken Vanishing Cabinet.
Also known as: Room of Requirement, the Room of Hidden Things