In northwestern London lies Kings Cross Station, a Muggle railway station that is one of the busiest in the city. It’s a perfectly ordinary station, with big plastic numbers over each track and guards who have never heard of Hogwarts School (PS6). However, every September 1, as the clock overhead approaches eleven o’clock (CS5) and the InterCity 125 pulls into platform nine (PA5), a strange crowd turns the occasional Muggle head. The crowd is wizarding children, bearing enormous trunks and caged owls, making their way toward – and then through – the solid metal barrier between platforms nine and ten (OP10).
The station was built by Muggles in the 1850s, and the Minister for Magic at that time, Ottaline Gambol, hit upon the idea of magically creating a platform in the new station to be accessed by witches and wizards wishing to board the Hogwarts Express (Pm).
After being hit with Voldemort’s Killing Curse in the Forbidden Forest, Harry Potter found himself in a place that vaguely resembled Kings Cross – a “limbo between life and death” (BLC) – where he met and talked with Albus Dumbledore. The Kings Cross that Harry encountered here was, as he described, “a lot cleaner and empty,” and with no trains. As Dumbledore explained, the encounter “of course” took place entirely inside Harry’s head – “but why on earth should that mean that it is not real?” (DH35)
A trip to the real Kings Cross Station reveals that platforms nine and ten that do not closely match the description in the books. J.K. Rowling has explained the error:
"I wrote Platform 9¾ when I was living in Manchester, and I was actually thinking of Euston. So anyone who's been to the real Platforms 9 and 10 at King's Cross will realise they don't bear a great resemblance to the platforms nine and ten as described in the book, and that would be because I was thinking of Euston at the time (HPM)."
The platform actually used for filming at King's Cross Station in the movies is Platform 4. Hagrid and Harry are also filmed walking over the pedestrian bridge across the tracks.