Known for its iconic cobble-stoned roads lined by shops displaying items that every 11 year old dreamed of owning, the diagon alley is a shopping alley from the wizarding world of the harry potter series. It is located in London, England behind a pub called the Leaky Cauldron and is only assembled by the wizarding community being completely hidden from the muggle world. The Diagon Alley can be accessed by tapping the correct brick in the wall behind the Leaky Cauldron (from the rubbish bin, three up and two across) causing the wall form a large archway for entry. It can also be accessed by Floo Powder and Apparition and given the ever surprising nature of magic there may be other entrances as well.
This alley was first mentioned in the philosopher's stone when Harry received a letter to Hogwarts and found out about his lineage.
"There were shops selling robes, shops selling telescopes and strange silver instruments Harry had never seen before, windows stacked with barrels of bat spleens and eels' eyes, tottering piles of spell books, quills, and rolls of parchment, potion bottles, globes of the moon..."
—Harry Potter visits Diagon Alley for the first time
Here one can find every item off their hogwarts supply list and much more. It houses shops such as Florean Fortescue's Ice Cream Parlour, a beloved ice cream parlour, Flourish and Blotts, a popular bookshop where most Hogwarts students purchase their school books, the trustworthy Gringotts Wizarding Bank run exclusively by goblins, Madam Malkin's Robes for All Occasions and many more.
The Diagon Alley connects to a second, less reputable shopping district, Knockturn Alley. As opposed to the vibrant and bright Diagon alley the Knocturn is more dark and sinister with its regular visitors being those interested in buying artifacts needed for practicing that dark arts which could be found for sale over here.
Over the series the alley has been mentioned multiple times with it being affected and changing in nature as the dark lord slowly took over the wizarding community.