The Hogwarts Express in J.K. Rowling’s books departs from Platform 9¾.
The platform is located in the fictional magical space between platforms 9 and 10 at London’s King’s Cross railway station. Young witches and wizards reach it by running directly at the barrier between the two platforms. The Hogwarts Express then carries students north to Hogwarts at the beginning of each school year.
Harry first learns how to find the platform in Harry Potter and the Philosopher’s Stone. He asks the Weasley family for help at King’s Cross, and Mrs. Weasley explains the unusual method of entry. The scene introduces readers to the practical boundary between ordinary London and the wizarding world.
King’s Cross later installed a real Platform 9¾ photo point for visitors. The actual station’s platforms 9 and 10 were separated by tracks, so the film production used nearby platforms 4 and 5 for some railway scenes. The fictional platform is therefore not an ordinary numbered platform.