For 14 years Mr Lewis has been guiding his tour groups beyond Sydney's architectural giants of the Harbour Bridge and the Opera House to landmarks that probably don't register higher in most people's minds than as points of orientation as they rush about the city.

A second look, however, reveals enduring monuments to Sydney's twentieth century industrial and economic past.

Like the Readers Digest building in Surry Hills, which was designed to house one of Australia's biggest computers of its time.

Opened in 1967 the $1 million computing behemoth sat in a specially designed central vault overlooked by an internal staircase.

"It was basically a building built around a computer," Mr Lewis said. "The idea of the building was that from every floor you can see this glistening machine."

The computer, which processed the magazine's massive mail order system, is long gone along with Reader's Digest operation.

But architect John James imposing building of chiseled concrete and decorative iron grills, inspired by 12th century gothic cathedrals, remains an imposing landmark among the inner-city terrace houses.

Turn back the clock 50 years and head north until you hit the water and you find what were the largest timber structures in the world for their time. The Woolloomooloo and Walsh Bay Finger Wharves.

THE FORGOTTEN LANDMARKS

While other big harbour cities such as New York, San Francisco and Rotterdam were building steel finger wharves, architect Henry Deane Walsh chose the plentiful supplies of hard wood available to build new wharves for Sydney.

"It was absolutely cutting edge from 100 years ago," Mr Lewis said. It was also enduring, with Woolloomooloo's 410 metre finger wharf retaining it's title of the longest timber-piled structure in the world. With the rise of the shipping container in the 60s - which revolutionised who cargo was transported - the wharves looked set to be washed away into history.

But the public fight to save the wharves has reinvented them with the Sydney Theatre Company moving into Walsh Bay and Woolloomooloo transformed into a fashionable precinct of restaurants, residential apartments and a hotel.

Sydney Living Museums assistant director Caroline Butler-Bowden said we need to find new love for our other mothballed landmarks of twentieth century industry so they can be saved, like the finger wharves. "Sydney Harbour is dotted with overlooked landmarks that have long passed their use-by-date," she said.

One of those is the hulking mass of the old coal-fired power station at White Bay, Rozelle.

"Many of our 19th century landmarks we now love and the battle for them has been won. It is up to us as Sydneysiders to come up with radical new ideas to make key landmarks of the twentieth century work."

Sitting on a huge block of land right on the water the White Bay Power Station would be an attractive site for developers but the State Government has earmarked it for cultural use.

Now it is just a matter of figuring out what it will become. Hopefully inspiration will be drawn from some of our other overlooked landmarks such as the Willoughby Incinerator - designed by Walter Burley Griffin - that has been turned into an art space and cafe.

Or the huge quarry at Olympic Park - where at one time 60 percent of Sydney's trademark red house bricks were manufactured - which has been turned into a wildlife sanctuary and high-rise nature walk.

In November, the State Government will hold a summit that will include reinventing White Bay Power Station.