Of the many fascinating things about Tempelhof, one is that juxtaposition of events, little more than a decade apart. The Airlift, lasting nearly a year, established it as a symbol of what used to be called the Free World, and today it is virtually a monument to that event. This effectively sanitised its earlier history as a triumphal example of Nazi-led technological innovation, opened just before the Second World War as a component of the Speer/Hitler plan for the rebuilding of Berlin. It was designed to last until the year 2000. Somewhat surprisingly, it has. It is the only major airport in the world to have remained virtually unchanged over more than 60 years. What can it teach us?

I have never yet flown into Tempelhof - there are no scheduled flights there from Britain - but when I am in Berlin, I try to go there. The food is excellent, the atmosphere wistful, the whole place is in good order but a little dingy. It should not really be here at all: a big airport, only two miles south of the city centre, and scarcely used. If more people knew about Tempelhof, they would demand to come here rather than the more distant Tegel. A few commuter planes hop in and hop out again - it is a domestic-flight sort of place, where most of the hardware on display has propellors.

It is here by an accident of history. The landing-field was originally a Prussian military training-ground, first converted to an airport in 1923, when the Weimar Republic commissioned a handsome modern terminal by Paul and Klaus Enger. This was designed for expansion, but was demolished after ten years and replaced by the present building. The reason given was that it was in the wrong place, and it may have been. But it was also insufficiently grand, and in the wrong style, for the Third Reich.

Today, Tempelhof stands in the way of the new Berlin. It is a big open space in the map, the city wrapping round it. To the north, the frenzy of Berlin's reconstruction continues at a high level - new roads, new railways, the entire jigsaw of Potsdamer Platz being pieced together across what was the Death Zone of the Wall, a new government quarter being built, Daniel Libeskind's Jewish Museum finally opened, the Reichstag re-fettled and reopened with its glass dome by Sir Norman Foster. Down at Tempelhof, just south of the one-time Bohemian quarter of Kreuzberg, there is none of that. Not yet. Things are quiet. Buses serve it, but the metro system was never connected directly, meaning that you have to walk an inconvenient distance in the open from station to terminal. There are rumours that Tempelhof will be closed down and redeveloped. Arguments fly as to what, precisely, this redevelopment should be. In the meantime, it is there: a part of history that went on living, like a coelacanth.

You will find it in very few books on architectural history. Perhaps this is because it is tainted by its style. Maybe the skin of the building is deemed to be all wrong for its function - airports, which are usually in a permanent state of rebuilding, are the one crucial building type of the 20th century, and are nearly exclusively modernist, almost never classical. Perhaps there is a lingering discomfort over the politics of its genesis: the feeling that nothing of merit should ever be found in Nazi-era architecture, that it must be put in the same box as kitsch Nazi-era paintings. These factors may have weighed in the balance in the past. But I think Tempelhof is little-known simply because it is overlooked, sidelined, off-pitch. It is enormous - I am told that, as an office complex, it is second in size only to the Pentagon, and it certainly looks that way on the map - but it is curiously invisible.