Diagon Alley is a hidden street in the wizarding world of Harry Potter, located in London. It is accessible through a brick wall at Leaky Cauldron, a pub for witches and wizards. The alley is filled with shops that sell magical items, including wands, potions, and robes. Visitors to Diagon Alley can find famous stores like Ollivanders, known for its wands, and Gringotts, the wizarding bank. The alley serves as a central hub for wizards to purchase supplies and gather information, making it an essential part of their magical lives.