about
What's this about? Diagon Alley (a play on the word "diagonally") is a fictional High street located in London. It is accessible to the wizarding world, to which it is something of an economic hub, but hidden from Muggles. However, Muggles are allowed access to it if they need to accompany their Muggle-born magical children. If a wizard or witch needs something, chances are that it can be found in Diagon Alley.One entrance to Diagon Alley can be reached on foot by passing through The Leaky Cauldron. The inn, invisible to Muggles, lies somewhere along the London thoroughfare Charing Cross Road, between a bookshop and a record shop. To reach Diagon Alley, one must go through The Leaky Cauldron to a rear courtyard and tap a brick in the wall, found by counting three up and two across, three times. Given the busy nature of the area, travelling to and from Diagon Alley is likely typically done by more magical means such as Apparition or by using the Floo Network.
found on wikipedia.org