Most of the interiors were built on stages at Leavesden, north-west of London, but a surprising amount of the films was shot in real buildings that are open to visitors. Several English cathedrals stood in for the school's corridors and courtyards — their cloisters are the ones you remember from the early films, and they are working religious buildings you can walk into on an ordinary afternoon. A castle in the north of England provided the courtyard used for flying lessons. In Scotland, a curved railway viaduct carries a working heritage steam service across a valley; the train in the films crosses it, and you can ride the same line in summer. In London, the station used for the departure scenes is a mainline terminus you can walk through for free, and the alley used for the wizarding shopping street is a narrow Victorian lane near the Thames. A practical note for anyone planning a trip: the film sets themselves no longer exist as sets — the studio tour near Watford preserves them as an exhibition, which is a different experience from standing in a place that was already there and will still be there when the films are forgotten. If you want the latter, go to the cathedrals and the viaduct.