Welcome to Harry Potter Theory. Today, we’re going to be unpacking one of the more mysterious aspects of Harry Potter- the department of mysteries. Honing in further, we’re going to be taking a look at the peculiar workers of this department- Ministry employees known as The Unspeakables. We’ll also be looking at, later in the video, all of the rooms / chambers that reside inside the Department of Mysteries.
The ministry of magic is the primary form of government in the magical world - at least in the UK. Like a muggle government, the ministry’s responsibilities are vast, as they are the primary body that attempts to sustain law and order in the magical world. Like any system of government, in an effort to cover as much ground as possible, the primary governmental body is systematically divided to focus on different sectors of the wizarding world. 
These ‘sectors’ or ‘departments’ cover the more common areas like the Department of Magical Law Enforcement and the Department of Magical Transportation, but there are also OTHER departments reserved for less..obvious pursuits. Queue level 9 and the Department of Mysteries.
The department of mysteries is responsible for studying the mysteries of the wizarding world, mysteries associated with love, space, thought, time, death, and other things. Basically anything that is unknown. Anything pertaining to this department is highly confidential, and those who work in this department are referred to as ‘unspeakables’. The divisions of this department are broken up by area of study, and includes the following: The brain room, the hall of prophecy, the death chamber, the love chamber, the space chamber and the time room. These rooms are accessed via the ‘room of doors’ - a large circular room where everything is black.
What’s particularly curious or dare I say..Mysterious about the Department of Mysteries is that it actually preceded the existence of the Ministry itself. The Ministry was established in 1707 and the Department of Mysteries had activity as early as 1672. The name checks out.