The Department of Mysteries is part of the Ministry of Magic, found on level nine. The work of the department is top secret, and workers there are known as Unspeakables. The job of the Department is to study such things as the mind, universe, death and love.
Rooms in the Department can be accessed from a circular room with identical doors all around it. When someone enters this room the doors spin around, confusing an intruder. However if you ask for the exit, it will open the correct door for you.
 The Time Room
This room is full of clocks. There's a large crystal bell jar which appears to be full of glittering wind. A tiny bright egg starts to rise in the jar, releases a humming-bird, falls back down and ages until it sinks to the bottom where it is enclosed in the egg again. When a Death Eater's head fell through the jar, his head alone became that of a baby and stayed in that state when he pulled the jar off. It is also here that the Time-Turners are stored, though they were all destroyed during the Battle of the Department of Mysteries.
 The Planet Room
This is a dark room full of planets. When people go through it they sometimes just float in the darkness.
 The Brain Room
This room contains a glass tank full of brains, with ribbon-like trails made up of moving images like roles of film that are thoughts. When Ron Weasley summoned a brain to him, these thoughts attacked him like tentacles and left scars. Diffindo was unable to break them.
 The Death Room
A rectangular, dimly lit room like an amphitheatre, with a twenty foot pit in the middle containing a raised dais with an ancient stone archway. Inside the archway is a tattered, black veil which flutters slightly, and those who have more faith in the afterlife can hear voices behind it. In this room the Unspeakables study death. J. K. Rowling has made it clear that it was not used for executions.
 The Hall of Prophecy
Copies of hundreds of prophecies are labelled and kept in the Hall of Prophecy. They are each contained in what looks like glass orbs, which when broken will produce a ghost-like figure of the one that made the prophecy, who will speak it out loud. Only those people about whom a prophecy is made can retrieve one from the Hall.
 The Locked Room
This room is dedicated to the study of love. It is kept locked at all times. During the Battle of the Department of Mysteries the members of Dumbledore's Army tried to use Alohomora and Sirius' Knife on the door, but were unable to break in. See Additional Canon below.
 Known Employees
 Battle of the Deparment of Mysteries
During his fifth year at Hogwarts, Harry Potter repeatedly had dreams of himself walking through the Department of Mysteries, that were put into his head by Voldemort. Voldemort wanted Harry to enter the Hall of Prophecy in order to steal a particular prophecy concerning the two of them. These dreams showed Harry where to go. To give Harry extreme motivation to break into the department, Voldemort showed a final vision of himself torturing Sirius Black in the Hall. Harry and five others went to London to rescue Sirius after finding that no Order of the Phoenix members could help them.
The six students eventually managed to find the Hall of Prophecy, however the vision was soon proved to have been an invention and they were ambushed by Death Eaters. To escape, they broke prophecies around them to create a distraction then attempted to flee. They were able to temporarily incapacitate a number of Death Eaters, but eventually only Harry and Neville Longbottom were left standing, now in the Death Room. Neville was taken hostage, but before Harry handed the prophecy over they were rescued by members of the Order of the Phoenix and Albus Dumbledore himself. Sirius Black was killed there and fell behind the veil. Only Bellatrix Lestrange escaped the Department and Harry chased after her into the Atrium, where shortly after Dumbledore and Voldemort arrived and duelled.
See also Second Wizarding War
 Additional Canon
 The Locked Room
J. K. Rowling was asked in a PotterCast interview about the locked room. She clarified that this room is the one dedicated to the study of love. It contains a fountain or a well with a powerful Love Potion inside. Witches and wizards would take it and study the effects. It needed to be locked because the power of love is one of the most dangerous forces.
- ↑ 1.0 1.1 The Leaky Cauldron and MuggleNet fan websites interview with J. K. Rowling (2005), The Leaky Cauldron and MuggleNet Interview Joanne Kathleen Rowling
- ↑ 2.0 2.1 PotterCast episode 131, Rowling Along
- ↑ 3.0 3.1 3.2 J. K. Rowling, OotP 34
- ↑ 4.0 4.1 J. K. Rowling, OotP 36
- ↑ 5.0 5.1 5.2 5.3 5.4 J. K. Rowling, OotP 35
- ↑ Harry, A History website, Vault 27, More About that Veil
- ↑ J. K. Rowling, OotP 37
- ↑ J. K. Rowling, OotP 31-34