Location from harry-potter-order-of-the-phoenix by
The most secretive department in the Ministry, located on the lowest level -- containing rooms devoted to love, death, time, space, thought, and prophecy. The site of the climactic battle where Sirius dies and Voldemort is finally seen.
Harry has been dreaming about this place all year. A long dark corridor, a door at the end, and behind it something Voldemort wants desperately. The prophecy -- a glass sphere labeled with Harry's and Voldemort's names, resting on a shelf in the Hall of Prophecy among thousands of others. The Battle of the Department of Mysteries is the climax of the year. Harry, Ron, Hermione, Ginny, Luna, and Neville fly to the Ministry on Thestrals, navigate the spinning rooms, find the prophecy, and walk into a trap. Death Eaters surround them. The students fight with everything the DA taught them -- and they hold. They hold against adult dark wizards until the Order arrives. The Veil is in the Death Chamber. It is ancient, it whispers, and those who pass through it do not return. Harry can hear voices behind it. Luna can too. Sirius falls through it during the battle, hit by Bellatrix's curse, and the veil swallows him with the finality of a closing door.
A series of dark, circular rooms accessed by a plain black door at the end of a corridor on Level Nine. The entrance room spins to disorient visitors. Beyond it: the Hall of Prophecy with towering shelves of dusty glass orbs, the Brain Room with floating tentacle-brains, the Time Room full of clocks and a bell jar with an endlessly aging hummingbird, the Space Room full of darkness and planets, and the Death Chamber -- a stone amphitheater containing an ancient crumbling archway with a fluttering black veil.
Also known as: the Department of Mysteries, Department of Mysteries, the DOM