The x-rated X-Rated at the Canberra Museum & Gallery (you must be 18 to go into the temporarily "adults only" part of CMAG that's showing it) contains an unforgettable picture of the tower wearing a condom. Several other dignified Canberra landmarks, for example the Carillon and the eternally spurting (and very Freudian when you-think-about-it) Captain Cook Memorial Jet, are similarly dressed. The portrayals are part of a witty Cover Yourself In Canberra series of explicit but witty posters promoting safe, condom-employing sex.

The exhibition's curator Rowan Henderson, taking this reporter on a sometimes blush-making (for me) sneak preview of the show explains that X-Rated is about the history of the sex industry in the ACT. This is a proper subject for CMAG to tackle, she insists, because once upon a time, for reasons X-Rated explores, Canberra and the sex industry (pornography and prostitution) were conjoined in the popular imagination. Wits called the national capital Pornberra.

"So we're looking at sex work, formerly called prostitution, and at pornography, and at their surrounding industries. We just thought it was an interesting topic, a side of things in the ACT that hasn't been been looked at."

Canberra's fame as the porn-distribution capital of Australia was entirely earned.

"In X-Rated we look at the history of how the X classification came into being. When in the 1980s video-taping and video tapes became available for people in their homes suddenly people could watch pornography at home, instead of going out to a cinema or somewhere."

Of course, every film shown in a cinema has a classification and now the federal government, faced with this new phenomenon, had to invent a way of classifying these films people were going to watch at home. The government decided on an X-rating for sex videos.

But then up rose God's ambassadors to Australia the Reverend Fred Nile with his Festival of Light. A Festival newspaper advertisement in the exhibition thunders "Keep Video-Filth Out Of The Home! Say YES to GOD and GOODNESS." The local sex industry countered with its own, echoing advertisement, "Keep Fred Nile Out Of Your Bedroom".

"They [Nile and his disciples] campaigned against the introduction of the X-rating," Henderson says, "saying the videos contain not only sex but violence. Then all the states decided to ban the sale of X-rated videos in their states. But the federal government still controlled the territories, and it allowed the sale of X-rated videos in and from the ACT." By 1985 only the ACT and the Northern Territory allowed the sale and hire of X-rated videos, she says. "And so all the X-rated film distributors moved to the ACT."

More precisely, they moved to factory-style premises in Canberra's Fyshwick. There they churned out copies of videos using great banks of VCRs (in the exhibition there's a striking picture of one of these premises). This was an orgy of duplicating and, appropriately, sex industry entrepreneur John Lark called his video company Capital Duplicators. By the late 1980s, Henderson calculates, the making and selling (to all of Australia by mail-order) of pornographic videos was the ACT's fifth largest industry. It employed 300 people. To avoid any accusations that the videos contained violence the makers scrupulously scrubbed the movie clean of everything ("even pirates having sword fights" Henderson says) that might give Nilesque critics any ammunition.

At its peak, in the late '80s and early '90s, the Canberra-based sex video industry used to generate $34 million a year. Today, usurped by internet sex material, the Australian porn video industry (only about 20 per cent of it now based in Canberra) earns only about $2 million.

Some of those early local distributors began to make as well as distribute films. Lark created his Down Under series (he imported a US director rejoicing in the name John T. Bone), filmed in and around the Canberra region. CMAG, being cautious, is not showing any clips from any of these epics, but there are some stills from some of them and even photographs of camera and sound crews (well rugged-up against the cold) capturing the acts of the goose-pimpled actors. Why the lovers in some locally made films are engaging in acts of love in the Canberra outdoors, in such uncomfortable and unsexy places (for example on bridges and at the rubble-strewn Canberra Brickworks) is an amusing mystery.

Exhibits in the sex work chapter of the exhibition include a Little Red Book that this naive reporter picked up and began thumbing through (you won't be able to do this at X-Rated), unprepared for the horrors within. In several languages (for sex workers are often from overseas) it is among other things a sex worker's field guide with coloured photographs (the book is in use in all ACT brothels) to diseases a male customer's genitals may be displaying. The well-informed Henderson says every sex worker always examines her potential client's wedding tackle (this reporter's colloquialism, not curator Henderson's) before a transaction begin. Once seen, these diseased penis pictures are (just like the Black Mountain Tower sheathed in its condom) very hard to winkle out of the memory.

The term "sex work" is used throughout the exhibition and Henderson says this was done, and the word "prostitution" barely used, "out of respect" for the members of the world's oldest profession. The word "strumpet" doesn't get a mention and almost the only time the word "whore" occurs in X-Rated is on a big, bold, campaign button issued by the Scarlet Alliance. It proclaims "I Am A Whore And Proud".

Sex work has a long history in the ACT but X-Rated has the most to say and to show about what has come to pass, up to the present day, since self-government.

"Prostitution was illegal in the ACT until 1992," Henderson says. "But after self government the Assembly decided to do a review of the industry. There were worries about the spread of HIV in the community and suspicions it was being spread though the sex industry, which was found to completely false. But as part of that they recommended that sex work be legalised and regulated, as the best way to control it, and to control the health aspects."

After the Prostitution ACT of 1992 was passed an industry consultative group began to work on ways to make sure that the transactions of health workers and their clients were as safe as possible. Governments and sex workers' alliances combined in this and continue to do so. Lots of the material in X-Rated, including the AIDS Action Council's posters of Black Mountain Tower in its condom (with a witty play on ideas of "transmissions" of radio waves and of HIV) is of this health-promoting kind.

Other star exhibits include a series of hilarious but seriously intended cartoons that the ACT government commissioned Canberra Times cartoonist Geoff Pryor to do. Each cartoon ("It has the government logo in the corner" Henderson pointed out) was hung in every brothel where every client would see it and get its message. One cartoon promises a leering client something "very special" if he tries to have sex without a condom and the next panel reveals that the something very special will be his being kicked out, stark naked, on to a Fyshwick pavement in the dead of night. In another, a client who has shown up in an unclean, and unhygienic state is being told that, no, he can't have sex with one of the girls but might like to try his luck with Millicent, the brothel's foul (and foul-tempered-looking) goat.

Sex work exhibits in X-Rated include an unforgettable pair of black, shiny, knee-length boots that were worn by a sex worker ("they were her work boots" Henderson says) perhaps while plying the trade of a dominatrix. Wincing a little, this reporter thought what stories those boots would tell if only they could speak, surely speaking in curt, do-as-you're-told tones.

Canberra is liberal and largely post-wowser now, but pornography and sex work are still contentious subjects. There are members of the Legislative Assembly who want to see sex work stopped altogether using the "Swedish Model" that makes it a crime to buy sex. Then there are sex workers, working alone from suburban premises because the law only allows one sex worker per venue, today campaigning for a change of law so that (for safety's sake) there can be two of them on the premises. Aware of the ongoing controversies, Henderson is keen to say that X-Rated is not an exhibition with a point of view.

"We're about education. Sex and Canberra are very intertwined in people's minds and so the intellectual starting point for X-Rated was asking 'Why?' I don't think many people do know why; but it did come out of that 1980s classification furore. So we're just trying to educate people about that, and what the situation is now."

So as not to transmit any offence to any of the offendable, the normally family-friendly CMAG is taking extraordinary pains to hide X-Rated from everyone but those 18 and over, who on purpose go to see it. It is upstairs in a kind of sealed section of CMAG.

X-Rated - The Sex Industry In The ACT opens on March 28 at the Canberra Museum & Gallery, Civic Square. Entry 18 and over and it ends on September 20.