Take a deep breath before climbing Sydney Harbour Bridge.(The Orlando Sentinel)

Byline: Arline Bleecker

Clambering along a narrow catwalk on the Sydney Harbour Bridge is a sobering thought. So you'd better be sober if you want to venture to the bridge's dizzying summit _ 441 feet above the water _ for a spectacular 360-degree view of the harbor and surrounding metropolis.

In fact, this morning excursion, offered during Seabourn Cruise Line's calls in Sydney, Australia, is guaranteed to literally take your breath away _ at least for analysis. The half-day outing requires participants to pass a Breathalyzer test before setting out _ or up, as the case may be.

As landmarks go, the bridge is almost as well-known to Sydney visitors as the city's sail-shaped opera house. From a distance, it's quite common to see several clusters of walkers _ like a line of ants on a tree stump _ scrambling up or down the bridge's arched profile.

This may not be the excursion of choice for someone who can't bear to even watch Alfred Hitchcock's "Vertigo," but it sure sounds like fun for the venturesome. And those who have done it give Bridge Climb, which operates the tour, high marks for being efficient and well-organized.

Once you've passed the breath test, administered by Bridge Climb to ensure you haven't been imbibing, you and other participants will be outfitted in gray jumpsuits and belts, which secure you to the bridge. Then you'll be divided into small groups and briefed on safety.

While waiting your turn to climb, you'll view a video about what to expect, which includes a reminder to visit the loo before starting out; after all, it's a three-hour climb. Then you'll get to practice walking up and down a simulated section of the bridge to get a feel for it. Finally, you'll be given a walkie-talkie receiver so you can hear your guide while on the bridge, which locals affectionately call "The Coathanger." And you're off.