Top of the town rung by rung

SIMON HENDERY and photographer GLENN JEFFREY try out a new thrill climb - to the Southern Hemisphere's highest crow's nest.

During the eerie 37m climb up the ladder inside the Sky Tower's mast it's easy to forget where you are.

As you glance up at the mass of steel, ropes and cables disappearing into the gloom, it seems odd to think you are in a concrete cylinder high above Auckland's streets.

But 10 minutes later, stepping out onto a "crow's nest" platform 270m above the ground, your sense of place comes crashing back.

Vertigo, a $95 guided tour to half-way up the Sky Tower mast, opens to the public on April 22.

Groups of up to five thrill-seekers will be taken to the highest viewing platform in the Southern Hemisphere during the 130-minute trip.

Only a handful of Northern Hemisphere buildings and towers offer higher vantage points.

Martin Lekner, a director of Vertigo operator To The Top, said it had taken more than two years to plan the venture and get the necessary approvals.

Climbers will be harnessed throughout their climb up the mast's internal ladder - which begins above the tower's upper observation deck - and during their time on the crow's nest.

Climbers will be breath-tested at the start of their trip and the climbs will proceed only when winds up the tower are below 70km/h.

A climb up a practice ladder at the base of the tower will be used to weed out anyone likely to suffer an attack of vertigo.

Mr Lekner, a former executive of the company that managed Sky City's construction, said he was inspired to set up the climb after experiencing the Sydney Harbour Bridge climb and deciding Auckland needed a similar thrill climb.

"I immediately thought of the tower because it's a high vantage point and it was a structure I knew about.

"I had a good idea it would be rated and approved for public climbs."

The climb has no age restrictions, but Mr Lekner says participants will need "a moderate level of fitness".