The Harbor Bridge in Sydney

Completed in 1932, the bridge is unquestionably one of the most famous of that famed city's landmarks. Coming in the middle of the Depression, which was world-wide not merely in the U.S., it was an economic as well as an engineering marvel.

Prior to the bridge the only routes between the center of Sydney in the south and the outlying residential areas in the north were by ferry or a 20km road. The road route required traversing five bridges.

Known locally by some as 'the coat hanger', it is a double-arch style, anchored on both sides of the harbor, with a flat road running beneath the arches. Arches are tied together with short trusses, forming a strong and attractive web. Like many bridges, it brilliantly combines esthetic beauty and technical ingenuity.

Among its many clever aspects is a hinging mechanism at each end that allows the steel structure to expand and flex without cracking. Due to thermal expansion the peak of the arch changes by as much as 18cm/7in. Turning the Golden Gate on its head, so to speak, the roadway runs under the arches, not above them.

Construction began at the end of 1926, with foundations 12m (39ft) deep, set in sandstone, and the arch spans 503m (1650ft). Not the world's longest single arch bridge, even at the time, it is one of the most beautiful, owing to its elegant simplicity and the setting.

Thanks to the six million rivets and the 58,000 tons of steel it is, however, one of the heaviest of its kind. In order to test the load bearing capacity, nearly 100 locomotives were positioned along the roadway in 1932.

By today's standards the 6.25 million Australian pounds ($12.5M) construction cost seems modest, but at the height of the Depression it was a substantial sum. It was paid off - by tolls that started at 6 pence (5 cents) and even now is only $3 - only in 1988. Today, more than 150,000 vehicles, which once included horses, cross the bridge daily.

The structure includes a lookout point, called Pylon Lookout, from which visitors can see the magnificent harbor, including the much newer Sydney Opera House.

But for those who want a real workout, consider joining the Bridge Club for a stroll. Thanks to the Bridge Club, founded in 1998, visitors can don suitable clothing and, tied to a safety line, actually walk over the arch above the roadway. The view is breathtaking. For the truly bold, there are even night climbs.

Entry is via the pedestrian walkway, reached via stairs from Cumberland Street at the edge of The Rocks. With some 200 steps to the lookout, visitors should be prepared for a healthy climb.