London King's Cross railway station

Where it sits. King's Cross occupies the north side of Euston Road in the London Borough of Camden, shoulder to shoulder with St Pancras and above one of the busiest Underground interchanges in Britain. It is the southern terminus of the East Coast Main Line, the railway that runs some 393 miles to Edinburgh by way of Peterborough, York and Newcastle. The site was previously occupied by a smallpox hospital and a fever hospital, and the name comes from a short-lived monument to George IV that stood at the crossroads until it was demolished in 1845. Lewis Cubitt's station opened in October 1852 for the Great Northern Railway: two vast arched train sheds of yellow London stock brick, each roughly 800 feet long and spanning about 105 feet, fronted by a facade of almost aggressive plainness — two great glazed arches, a screen wall and an Italianate clock tower whose mechanism came from the Great Exhibition of 1851.

The rebuild that changed the way it looks. For most of the twentieth century Cubitt's front was invisible, buried behind a low 1972 concourse of glass and steel that filled the forecourt with ticket queues and burger stands. The transformation came with a rebuild completed in stages between 2007 and 2013. John McAslan and Partners added the Western Concourse in March 2012: a semicircular white steel diagrid that springs from a single central funnel and sweeps roughly 20 metres overhead across some 7,500 square metres, at the time the largest single-span station structure in Europe. The 1972 shed was then torn down and King's Cross Square opened in front of the original brickwork in September 2013, revealing it properly for the first time in four decades. Behind the platforms, the 67-acre King's Cross Central scheme turned the old coal and goods yards into Granary Square, Coal Drops Yard and the Regent's Canal towpath.

On screen. The barrier run in Harry Potter and the Philosopher's Stone was filmed at King's Cross, but not at platforms 9 and 10. The real 9 and 10 sit in a plain suburban extension built in the 1970s, a low-roofed shed with no wall between them to run at. The production used platforms 4 and 5 instead, which stand under Cubitt's arched roof and are divided by a solid brick pier of exactly the theatrical proportions the scene needed. For Chamber of Secrets the crew simply renumbered 4 and 5 for the camera. The Nineteen Years Later epilogue at the end of Deathly Hallows: Part 2 was shot on the same platforms with the same brick arch. One further correction worth carrying: the grand Gothic exterior identified as King's Cross in Chamber of Secrets, the one the flying Ford Anglia climbs past, is St Pancras next door.

The photo spot is not the filming spot. A sign appeared on a station wall around 2003, and by 2005 half a luggage trolley had been mortared into the brickwork beneath it. The marker was shuffled around repeatedly during the long rebuild and was finally given a permanent home in 2012 in the Western Departures Concourse, outside the ticket gates and next to the Harry Potter shop. That means the trolley stands in a spot that is neither the real platforms 9 and 10 nor the platforms where the scene was shot — a third location entirely, chosen because it has space for a queue. Staff hand out house scarves and an owl cage, flick the scarf at the right moment, and an official photographer sells prints; taking your own picture costs nothing.

What else is worth looking at. Stand back in King's Cross Square and read the facade: the two arches express the twin sheds behind, arrivals on one side and departures on the other, an unusually honest piece of railway design for 1852. The clock tower is Italianate rather than Gothic, a deliberate contrast with Scott's hotel next door. The Great Northern Hotel of 1854, curved to follow the old cab road, was restored as part of the same works. Platform 0, opened in 2010 on the western flank, is one of very few in Britain. Outside the eastern side stand the German Gymnasium of 1865, built for the German Gymnastics Society and now a restaurant, and the Lighthouse Building of about 1875 on the Gray's Inn Road corner.

Getting there and timing. King's Cross St Pancras is served by six Underground lines — Circle, Hammersmith and City, Metropolitan, Northern, Piccadilly and Victoria — plus Thameslink beneath St Pancras. The trolley queue is shortest before about nine in the morning and after eight in the evening; on summer weekends the wait in the middle of the day can run past an hour. The concourse is fully step-free with lifts to every platform. Nothing here charges admission, which makes it an easy first stop on a walking route that continues to St Pancras, the British Library and the canal.