Department of Mysteries
Deep in the lowest level of the Ministry of Magic, on the ninth level, lies the Department of Mysteries. Here wizards who are called Unspeakables go about researching some of the deepest mysteries of existence. These wizards have discovered that there is magic that is inherent to the very fabric of existence which manifests itself in ways that are difficult to explain and even more difficult--if not impossible--to control. The Unspeakables explore and experiment with these mysterious forces in various chambers which are clustered around a circular room lined with doors.
Because of the secret nature of the work done in the Department of Mysteries, rumors arise about what goes on there. Luna Lovegood, believing The Quibbler, has stated that Cornelius Fudge "uses the Department of Mysteries to develop terrible poisons, which he secretly feeds to anybody who disagrees with him" (OP18). (There is no evidence that this is actually true.)
The Department of Mysteries is accessed via the lifts from the Atrium. A simple, bare corridor leads to a plain black door. This door opens into the circular room with twelve plain, black, handleless doors all around it. The room is lit with candles burning blue. The floor is polished so that it almost looks like standing water. When the door to the circular room is closed, the walls of the room revolve rapidly, making it impossible to determine which door is which. The doors open easily with a push out.
It is impossible to determine which door is which after the walls revolve (OP34).
The Brain RoomThis long, rectangular room is lit by lamps hanging low on golden chains from the ceiling. It is quite empty except for a few desks surrounding an enormous glass tank of deep green liquid. In this tank a number of pearly-white brains drift around. When removed from the potion in the tank, the brains fling out streamers of thoughts which can seriously injure someone if they wrap themselves around them. Other doors open off this room (OP34, OP35).
The Death Chamber(OP36) This room quite large and also rectangular. It is dimly lit. In the center is a sunken stone pit some twenty feet deep. Stone benches run all around the room and descend in steep steps toward a raised stone dais in the centre of the pit. An ancient, crumbling stone archway, unsupported by any surrounding wall, stands on this dais. This archway is hung with a tattered black curtain which flutters very slightly as though it had just been touched, althoughthe air in the room is still and cold. Some people can hear voices throught the veil; it would seem that those who have lost loved ones are the ones who can hear voices, but this has not been stated specifically (OP34).
The Hall of Prophecy(OP37) The Hall of Prophecy, which is entered through the entered through the Time Room, is a vast cold chamber, high as a church, filled with row upon row of towering shelves. On these shelves are hundreds of small, dusty, glass orbs, each with a yellowed and dusty label affixed below. Candle-brackets set at intervals along the shelves hold blue-flame candles. The row of shelves directly in front of the door from the Time Room is number 53. Number 54 is to the right of that, then 55, and so on. The light is very dim in the Hall. The candles are located on either end of each row, which means that from one end, the far end of each row is lost in darkness. Some of the orbs glow with a faint inner light but others are cold and dark. The Prophecy about Harry was located a short distance down row 97 (OP34).
The Locked RoomThe door to this room is locked and no spell or magical device appears to work to open it. Harry tried his magical penknife, which would open any lock, but the blade melted away and the door remained solidly locked (OP34). Inside this room, according to Dumbledore, is the most powerful magic of all: love. It is this magic, generated by his mother's sacrifice, that protects Harry. It is also this magic that drove Voldemort out of Harry when the Dark Lord tried to possess him (OP37).
Rowling's comments on the "Love Room":
The Planet RoomThis is a dark room full of planets, which even Luna Lovegood calls "a very odd place". Apparently something like the anti-gravity mist from the Triwizard maze is in operation at least part of the time, since people who have entered the room have reported that some of the time they were just floating in the dark (OP35).
The Time RoomThis room is filled with beautiful, dancing, diamond-sparkling light. Clocks can be found on every surface, "large and small, grandfather and carriage, hanging in spaces between the bookcases or standing on desks ranging the length of the room, so that a busy, relentless ticking fill[s] the place like thousands of minuscule, marching footsteps (OP34)." A huge crystal bell jar stands at the far end of the room, and it is from this that the sparkling light comes. The bell jar stands on a desk and appears to be full of a billowing, glittering wind. Inside the jar, rising and falling on the glittering current, a tiny object moves through an endless loop. The object is a small humingbird, but it isn't always a bird. At the bottom of its circuit, the bird is within its egg. As it rises, it hatches and grows into a mature bird by the time it reaches the apex of its path. On the way back down, it becomes a fledgling bird and then reenters its egg, which reforms around it. This progression of time repeats over and over within the jar. A large glass-fronted case stands against a wall within which many Time-Turners of various sizes rest on shelves.
The path through this room, toward the bell jar, is a narrow passage between the many desks. At the far end, where the Time-Turners are located, is another door which pushes to open.