Someone talks about writing a will — or having failed to do so — as the six-tonne glass cube on wheels called the Edge prepares to cantilever three metres out from the Skydeck, on level 88 of the city's tallest building, the 92-storey Eureka Tower. It takes just 47.3 seconds and you're hovering in the air, where you remain for four long minutes. At first the glass on the floor is opaque. Then it suddenly clears. You can't help looking straight down to where Mr Cockburn says a colleague suggested they paint the outline of a fallen body. Before the glass clears, you hear the sounds of creaking chains and breaking glass.

"We're trying to go … from comfortable to scary," Mr Cockburn says. Of why the bossa nova hit The Girl from Ipanema is playing, he says: "We're kind of sadistic, I suppose." We're 30 metres higher than the previous highest vantage point in Melbourne, the observation deck on the 55th level of the Rialto Towers. The 2.1 by 2.6-metre cube of glass and reinforced steel, likened to a "giant matchbox", is designed to take up to 12 passengers at a time and hold at least 10 tonnes. Organisers hope this world-first attraction will become one of Melbourne's biggest tourist drawcards. It will be open to the public from May 15, running from 10am to 10pm daily, except when winds exceed 70 km/h.

Visitors take a lift ($16.50 per adult, $11 concession, $9 children) that deposits you on the 88th floor in 40 seconds. There you can wander about and, for an extra fee ($12, $10, $8), enjoy "the Edge experience". "The ones who scream their hearts out when they get in this thing just make me so happy," Mr Cockburn tells media on a guided preview.

He dobs in several people who have declined to enter the cube. State Opposition Leader Ted Baillieu is one who apparently baulked at the prospect. "It's very, very safe," Mr Cockburn says. The experience is "fairly roller-coaster-like". He concedes that he has been trying to overcome a fear of heights. "I've been skydiving and bungee-jumping," he says. "Work on this project has almost cured me, but not quite."