The headquarters of the British Ministry of Magic are located deep underground, below the HM Treasury building and the Whitehall, in London, Great Britain. They are comprised of a very large, ten-story building, housing several offices, departments and courtrooms.

Although all the structure is underground, magical windows show whatever weather the Magical Maintenance Department chooses for the day, from bright sunshine to hurricanes. Lifts provide access to every level, except Level Ten, the Wizengamot Courtrooms, which is only accessible via a set of stairs from Level Nine, the Department of Mysteries.

The Ministry of Magic Health and Safety Regulations (345-01 & 346-01) exists to protect those on the premises.

'They were standing at one end of a very long and splendid hall with a highly polished, dark wood floor. The peacock-blue ceiling was inlaid with gleaming golden symbols that were continually moving and changing like some enormous heavenly notice board. The walls on each side were panelled in shiny dark wood and had many gilded fireplaces set into them. Every few seconds a witch or wizard would emerge from one of the left-hand fireplaces with a soft whoosh; on the right-hand side, short queues of wizards were forming before each fireplace, waiting to depart.

HARRY POTTER ENTERING THE MINISTRY FOR THE FIRST TIME' .

The Ministry of Magic is accessed through an abandoned red seemingly innocuous Muggle telephone box, where the Ministry of Magic can be reached by dialling 62442 (which spells 'MAGIC' on an alphanumeric keypad) . 

Visitors to the Ministry of Magic came to a broken-down red telephone box on a dingy street which had several shabby offices, a pub, and a wall covered with graffiti. When the telephone in the box was dialled (62442, the word M-A-G-I-C), the welcome witch's voice answered, not from the phone, but from the air, as if the person was standing right there.

Visitors were asked their business at the Ministry, upon which a silver badge popped out with the visitor's name and purpose of visit. Then the telephone box dropped down like a lift for about one minute, after which the visitor would be in the Atrium.

The Atrium

"They were standing at one end of a very long and splendid hall with a highly polished, dark wood floor. The peacock-blue ceiling was inlaid with gleaming golden symbols that were continually moving and changing like some enormous heavenly notice board. The walls on each side were panelled in shiny dark wood and had many gilded fireplaces set into them. Every few seconds a witch or wizard would emerge from one of the left-hand fireplaces with a soft whoosh; on the right-hand side, short queues of wizards were forming before each fireplace, waiting to depart."

HARRY POTTER ENTERING THE MINISTRY FOR THE FIRST TIME

The Atrium was on level 8. It was a large hall with fireplaces up and down both long walls. The fireplaces on the left were used for arriving employees, while the ones on the right were for departing employees. The floor was polished dark wood. The ceiling was peacock blue with golden symbols moving across it.

The Fountain of Magical Brethren was halfway down the Atrium. A group of golden statues, depicting a wizard, a witch, a centaur, a goblin, and a house-elf, spouted water into the surrounding pool of water. At the end of the Atrium was a set of golden gates, next to which was a security stand. Eric Munch was usually on duty here. He registered the wands of visitors. Another smaller hall was beyond the gates, where there was a series of lifts. The lifts provided access to the other levels, except the tenth.

Levels

On level one were the offices of the Minister for Magic and Support Staff.

On level two was the Department of Magical Law Enforcement.

On level three was the Department of Magical Accidents and Catastrophes.

On level four was the Department for the Regulation and Control of Magical Creatures.

On level five was the Department of International Magical Co-operation.

On level six was the Department of Magical Transportation.

On level seven was the Department of Magical Games and Sports.

On level eight was the Atrium.

On level nine was the Department of Mysteries.

Level ten could only be reached by the stairs to the left of the door which led to the Department of Mysteries on level nine. Courtroom Ten was first seen during Harry's first forays into Dumbledore's Pensieve, when he witnessed various Death Eater trials. Dungeon-like corridors led to Courtroom Ten. The walls of the courtroom were dark stone. In the centre of the room was a chair covered in chains that stood below rows of high benches on which the Wizengamot sat.