The wizarding train platform in J.K. Rowling’s Harry Potter books is Platform 9¾.
Harry and other students board the Hogwarts Express from Platform 9¾ at London’s King’s Cross railway station. In the story, the platform lies between the ordinary platforms 9 and 10 and is reached by passing through a barrier.
The Hogwarts Express carries students to Hogwarts at the start of the school year and returns them to London at the end of term. The platform therefore serves as a recurring gateway between the ordinary Muggle world and the wizarding world.
King’s Cross station has embraced the fictional location with a Platform 9¾ sign and a photo opportunity. The real station’s platform layout does not literally place a hidden platform between 9 and 10 in the way the books describe. The fraction is part of Rowling’s fictional setting.