The Hogwarts Express departs from platform 9¾ in J.K. Rowling’s Harry Potter books. The hidden platform is located at London’s King’s Cross railway station.
Wizards reach it by passing through the barrier between platforms 9 and 10. Harry first learns about the platform from the Weasley family, then boards the scarlet steam train for his journey to Hogwarts. The departure becomes a recurring ritual at the beginning of school years.
Platform 9¾ is fictional, but King’s Cross embraced its association with the series. A luggage trolley installed at the station lets visitors pose as though they are passing through a wall, and a shop nearby sells Harry Potter merchandise.
The fraction is written as three-quarters, not as a decimal. It is also not the same as an ordinary platform numbered 9 or 10. The magical platform’s unusual location is part of the story’s contrast between the hidden wizarding world and modern London.