"The Hogwarts Express was streaking along below them"

A journey on a train inspired J.K. Rowling to write the Harry Potter series. This is why the Hogwarts Express has been given an important role in most of the seven books. 

Platform 93/4 at King's Cross, visible only to witches and wizards, has fascinated fans ever since the first book was published. In fact quite a few have tried to pass through the wall between Platforms 9 and 10! This section of King’s Cross Station became so popular that its management decided to build a trolley into the wall so that fans and tourists could take souvenir photos.

Ironically, J.K. Rowling has admitted that after the first couple of books were published she realised she had made a mistake, describing the platforms at Euston Station instead of those at King’s Cross.