Vienna, just after the Second World War. The city is battered, hungry and split between four occupying powers. An American pulp writer, Holly Martins, arrives to work for his old friend Harry Lime, and is told that Harry has just been killed by a car. Then, one night, Holly sees Harry's face in a doorway. That's The Third Man, the 1949 film directed by Carol Reed from a script by Graham Greene, with Joseph Cotten as Holly, Alida Valli as Anna, Orson Welles as Harry and Trevor Howard as Major Calloway, the officer on Harry's trail. The street scenes were shot here in Vienna in 1948, and most of the interiors in London studios. This is an unofficial fan walk, not made with or endorsed by the filmmakers or the studio. We begin at that doorway, the film's most famous moment, and follow Harry to the square where he vanishes and the square where the trap is laid. Then we step back to the start of the story at Harry's flat, and further back to the hotel where Greene found the tale, before going down into the sewers for the ending. Spoilers throughout. It's one of our self-guided walking tours, about 3.4 kilometers from Schreyvogelgasse to the Third Man Museum.

Before you set off

The walking adds up to about 47 minutes, so allow around two hours with time at each stop. The route is paved and mostly flat, with a gentle slope at the start. The film's best scenes happen at night, so an evening start gives you the right shadows in the old lanes, but the walk works at any hour. Two things to plan around. The city's sewer tour, the Third Man Tour run by Wien Kanal, the city sewer authority, starts at stop six. It runs only in the warmer months and on certain days, and it has a minimum age of 12, so check before you go and book ahead. The Third Man Museum at the end is a private museum that opens to individual visitors on Saturday afternoons, so if you want to go inside, time your walk for a Saturday and check before you go. The start is a few minutes' walk from the Herrengasse subway station, and the Kettenbrückengasse station is closest to the end.

Harry Lime's doorway

You're on Schreyvogelgasse, a quiet lane that slopes gently downhill. Find number 8 and look at its doorway. Just along the lane is the house where Beethoven once had an apartment, but tonight we're here for a ghost.

By this point in the film, Holly Martins has been asking questions all over town. Everyone tells him his friend Harry Lime is dead, run over by a car outside his own flat. But the witnesses don't agree. Some say two men carried the body. Another says there were three, and nobody can say who the third man was. Holly keeps pushing, and the city keeps pushing back.

Then, late one night, Holly is in this lane. Someone is standing in the dark of this doorway. Light from a window falls across it, and catches the man's face. It's Harry. Dead Harry, very much alive. It's one of the most famous entrances in film history, and it happens right here.

Holly goes after him. Harry runs. The chase goes round the corner and up the Mölker Steig, the little lane just around the corner, and on into the dark streets of the Inner City.

Stand back across the lane and look at the doorway. It's an ordinary entrance to an ordinary apartment house. Somehow that makes the scene even better.

Harry is running, and we're following. Head down to the Freyung, the long, sloping square below, then cross it heading east into the big square of Am Hof. About seven minutes.

Am Hof

You're on Am Hof, a large square in the Inner City. In the middle stands a tall Marian column, a monument to the Virgin Mary. Now try to imagine it gone. In the film, you can't see it: the filmmakers seem to have hidden it behind props.

This is where Harry disappears. Holly chases the running figure into this square and loses him. Harry hasn't hidden in a doorway. He's slipped into an advertising column, one of those round street kiosks covered in posters, and inside it a stair leads down into the sewers. Under Vienna there's a second city of tunnels, and Harry knows it well.

You won't find that kiosk today. The column and its door no longer exist. Anna's apartment building also stood on this square in the film, and that's gone too. An office block stands in its place. The square was heavily damaged in the war, and it looks quite different now from the way it does on screen.

Here's the best part. The kiosk wasn't just a screenwriter's trick. Graham Greene had been told about real sewer entrances disguised as advertising kiosks, and that they were never locked. Who told him, and where, is a story waiting for you later on this walk, at a famous hotel.

Harry is alive, and now Holly has a choice to make about his old friend. The police want him caught. To catch him, they'll need bait. Walk east from the square through the old lanes to Hoher Markt. About five minutes.

Hoher Markt

Ankeruhr clock on Hoher Markt, Vienna

You're on Hoher Markt. In the center stands a baroque fountain, the Vermählungsbrunnen, the marriage fountain. Like Am Hof, this square was badly damaged in the war.

This is where the trap is set. But first you need to know why Holly agreed to it.

After the doorway, Holly does meet Harry, high above the city in a cabin of the Riesenrad, the giant Ferris wheel in the Prater park. It's a detour from this walk, but it's the heart of the film. The cabin close-ups, by the way, were filmed in a London studio, not on the wheel. Up there, Harry looks down at the people far below and shows how little their lives mean to him. Then comes his famous speech. In it, Harry argues that Italy under the Borgias had bloodshed and terror and still gave the world the Renaissance, while Switzerland had centuries of peace and gave it only the cuckoo clock. It's a cynical, brilliant little speech, and Greene didn't write it. Welles added it himself during the shooting, and Greene later gave him the credit. Welles claimed he had taken the idea from an old Hungarian play, though no one seems to have found it. And Harry had his facts wrong anyway: the cuckoo clock is generally credited to Germany, not Switzerland.

What Harry is selling is penicillin. In a hungry, damaged city, he sells it diluted on the black market, and people who are given it suffer for it, children among them. The police show Holly those children. That's when Holly decides. He agrees to be the bait.

So, one night, Holly waits for Harry, and the police wait for Harry too, out of sight in the shadows around the base of this fountain. Stand by its base and look out at the dark edges of the square. Harry comes, the trap is sprung, and once again he goes underground, for the last time.

We'll follow him down later. First, let's go back to where it all began. Head south from the square to the Graben, the wide pedestrian street, turn right and follow it, then Kohlmarkt, to Michaelerplatz. From there, follow the palace south along Reitschulgasse to Josefsplatz. About ten minutes.