The Ministry of Magic is the home of the governing body of the magical community of Great Britain and Ireland. Each level is home to the different departments of the Ministry of Magic;

Level 1 – The Minister for Magic & Support Staff
Level 2 – The Department of Magical Law Enforcement
Level 3 – The Department of Magical Accidents and Catastrophes & The Department of Education
Level 4 – The Department for the Regulation and Control of Magical Creatures
Level 5 – The Department of International Cooperation, & The Chambers for the International Confederation
Level 6 – The Department of Transportation
Level 7 – The Department of Magical Games and Sports, Bathrooms, & The Cafeteria
Level 8 – Atrium
Level 9 – The Department of Mysteries
Level 10 – The Wizengamot Chambers

The visitor’s entrance to the Ministry is a muggle red telephone box, near Great Scotland Yard, and by dialling 62442, visitors can enter. The Ministry Atrium can be found here