When we were kids, we believed there was a guest book hidden at the top of the Sydney Harbour Bridge to sign your name in if you managed to make the illegal climb up.

Also known as the Coathanger, the world’s largest single span bridge was there in the background as we kids threw up on the rollercoaster at Luna Park, the famous fun park nestled beneath its northern pylon. We passed beneath it on the compulsory high school harbour cruise – a rite of passage for any self-respecting teenager – and it cast an appropriate shadow for romantic rendezvous later on in life.

But now some of the mystery has dissipated. Over the past 18 months, the top of the bridge has been accessible to anyone with a sense of adventure – and without a serious fear of heights. Some 250,000 people have clamoured up and back to date.

On a recent trip back to Australia we noticed groups of moving specks along the arches on the way home from the airport. They were the groups of twelve or so people who leave to make the climb every ten minutes – traipsing over our precious bridge as if it were a mere tourist attraction!

After the initial indignation wore off, we decided we had to do it too.

A week later we are going through the comprehensive preparations that BridgeClimb, the company which runs the climbs, have designed. We’re breathtested, briefed, clothed, and taken through a practise run with our harnesses on a replica of a portion of the bridge before being let loose with our guide, Michael, who asks us if today is our first climb.

“That’s good,” he jokes as we chorus a yes. “It’s mine too.”

The clothing is an exercise in entanglement. Nothing can be dropped from the bridge onto the traffic below for fear of scaring – or killing – a driver. Glasses are roped in, two-way radios are buckled on, hankies on elastic are stuffed up sleeves and even jackets are folded safely into little custom-made bags attached to belts. My partner asks the guide if he needs a tether for his false teeth.

It’s time to do it. Walking single file along the narrow walkway heading to the pylon, I suddenly feel like we’re going way too fast as I look the twenty or so metres through the holey metal grille below me. Norma, a Scottish woman in her fifties trailing me, starts chatting about her husband and a hospice they volunteer for back in Scotland. They’re trying to raise money by doing this.

“Just tell me if I’m talking too much,” she sings out cheerfully. “I always talk when I’m nervous!”

“Shut up! Shup up!” I scream inside my head. I discover I prefer silence when I’m nervous.

Paul Cave, who opened BridgeClimb Sydney in October 1998, says about 30 per cent of climbers suffer from acrophobia, an abnormal dread of being in high places, but remarkably few are unable to “conquer the bridge and overcome their fear”.

“We put a lot of effort into safety,” he says. “I thought we’d be confronted with people freezing when they get up there, but we only get probably one or two people per month who pay but can’t commence the climb.”

I’m probably not quite one of those 30 per cent but am rather proud of myself when my knees stop shaking, the sweat on my brow evaporates and I can push on.

A series of ladders are climbed to reach the base of the bridge span itself, and at the top of this, the walkway becomes wider – and opaque, thankfully – and it’s plainsailing along the gentle slope to the summit.

Michael regales us with stories and statistics via the radio as we stroll in the late afternoon sun. Over 52,800 tonnes of steel covered in 272,000 litres of paint were used to build the arch and approach spans; 1,400 people were employed on the project during the eight years of its construction; the length of bridge, including approaches, is 1,149 metres; the water when we get to the top will be 134 metres below us; and approximately 6 million rivets hold everything together.

One of the folk tales my partner has heard is that the construction workers would hold the red-hot rivets in their pliers on boats on the water, and toss them up to workers on the bridge – who would catch them in their pliers before driving them in.

As the slope flattens out, the breeze is surprisingly soft and warm, and the colours of the harbour become cinematically intense as the sun slides towards the blurry Blue Mountains on the horizon.

The Olympic Stadium at Homebush Bay can just be seen to the west, while to the east, the harbour ebbs around dozens of bays and coves and flows into the deep blue of the Pacific.

Closer at hand of course are the white sails of the Opera House – now there’s an idea for an abseiling entrepreneur – and the harbour ferries, ploughing their way from Circular Quay to Manly, Balmain and other spots.

No cameras are allowed up but Michael takes digital snaps of individuals and the group at the summit.

It’s exhilirating and romantic as well. Cave says more than 100 marriage proposals have so far been made at the summit.

“I think people just get so emotional … they’re moved by the view and the euphoria. You get people frequently moved to tears, or quoting poetry, because they’re romantically moved.”

Then the helicopters start arriving, and we feel like we’re in an Australian Tourist Commission advertisement or at least promoting some sort of Australian breakfast cereal or margarine.

“When there’s a good sunset, photographers come out in force to get their shots,” Michael explains.

Then the Blackhawk arrives.

“They’re practising their anti-terrorist exercises prior to the Olympics,” Michael almost screams into his radio. I doubt any bridge climber is going to be a terrorist, but I almost start to feel terrorised as it seems like all these choppers are coming straight for us.

As we cross to the western frame, the traffic below is as thick as Sukhumvit on a Monday morning but moving somewhat faster. In 1995, the average daily traffic crossing the bridge was over 150,000 vehicles.

Cave spent seven years and millions of dollars refining the BridgeClimb concept, meeting stringent safety guidelines and gaining government approvals. An Act of Parliament was required to change a law dictating how close the public could get to a moving Sydney train.

Cave says he’s stopped trying to find comparisons between climbing the Harbour Bridge and reaching the top of the world’s other architectural wonders.

“Climbing the Bridge is unique – there is no reference point,” he says. “More than six million people have climbed the Eiffel Tower, but you basically go up most of the way in a lift. Fundamentally, you can’t climb structures like this anywhere else in the world. This is totally unprecedented.”

As we return to the ground down the western frame, we feel a little how we felt when we discovered Santa Claus wasn’t real: there was no guest book at the top in which to leave our mark after all.

And er, no marriage proposal.

Website: www.bridgeclimb.com
Prices: From AUD108 to 130, or AUD89 for children aged 12-16

/ Travel