First announced as the ''Administration Building'' on October 20, 1927, the structure was not completed until 1956 - a remarkable 29 years later.

Design work had begun as early as 1924. To put that into perspective, John Gorton, the future RAAF pilot and prime minister whose name was to be bestowed on the structure many decades later, was just 13 years old when it was conceived and a senator with seven years in the upper house behind him by the time it was finished.

The reasons for the delays, protracted even by Canberra standards, are not hard to find. The depression and then World War II claimed many casualties in the ACT and the flagship ''Administration Building'' was one of them.

There is irony in the way then prime minister Stanley Bruce announced the project:

''The policy of erecting public buildings of a temporary nature in Canberra was condemned by the Prime Minister (Hon S.M. Bruce) in a memorable speech this morning when he turned the first sod of the foundations of the first permanent administrative building to be erected in the Federal Capital,'' The Canberra Times reported on October 21, 1927.

''We all recognise the need for some temporary buildings; they were necessary for the effective transfer of the seat of government,'' he said. ''But now Parliament is established here we should concentrate on structures of a permanent nature, more in keeping with the ideals underlying the establishment of the federal capital city.''

The Administration Building's cost, originally estimated at £842,000, blew out dramatically over the years with a final figure apparently impossible to obtain.

It's most remarkable feature, the communications bunker first proposed in 1969 and not completed until 1976, cost almost $3.5 million (or about $40 million in today's money).

One of Canberra's worst kept secrets, the underground bunker, ceased to operate as the Department of Foreign Affairs and Trade's communications centre in 1996.

Holes have since been punched in the reinforced concrete roof to create small atriums that allow natural light to filter down to office space that is now used for a variety of other purposes.

Intriguing features, including fragments of a graffiti wall designed to boost staff morale, and the space-age foyer complete with stainless steel pillars and a ceiling that would not look out of place on the set of Barbarella, have been retained.

Visitors to the foyer can examine some of the keyboards and terminals, including a Typex that appears to be the bastard love child of Germany's Enigma machine and a 19th-century typewriter, that are displayed under glass.

''One time pads'', cipher keys allowing unbreakable coded messages to be sent from an embassy to Canberra and vice versa, have also been retained.

Of particular interest is some of the graffiti. Whatever happened to the wits who wrote: ''As I slide down the bannister of life, I shall always remember Foreign Affairs as a splinter in my arse''; or the more insightful: ''A neutron, a proton, a little yellow photon, a fission, a fusion and we all fall down''?

Other quotable quotes include: ''There is no rainbow at the end of the pot''; ''Help stamp out poverty, shoot a beggar''; and ''And the Lord said unto the shepherds, 'buzz off, this is cattle country'.''

Who says public servants don't have a sense of humour?