"Is it too late to change our minds about the Sky Tower?" wrote Peter Calder in a Herald columnin 1997. "From almost everywhere in the metropolitan area it can be seen, looming out of the landscape like a control tower waiting for an alien invasion."

How time changes. Next week, the Sky Tower turns 20 and it's impossible to imagine Auckland without its landmark.

Lead architect Gordon Moller says the tower is now widely accepted, appreciated and admired-and looks better with time.

"It was fun to design.I suppose one could describe it as a folly except it's one of those things you don't get to do too often. It does really well in terms of a business case," he said, referring to hundreds of thousands of visitors and its broadcasting and communication functions.

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"The Sky Tower was seen like a marker,a bit like a pou,for the city of Auckland, an anchor of the city,centre of the CBD,and we thought a lot-long and hard-about what the design should be like. We had are quirement to build a certain height for communications but also for the views that people would see, to appreciate the isthmus.

"I wanted an elegant tower, a beautiful tower that satisfied all the terms of the brief and that would last a long time and that people would be proud of."

At 328 metres tall the Sky Tower is the tallest man-made structure in New Zealand and the tallest free-standing structure in the Southern Hemisphere.

When it opened in1997 it was one of the 10 tallest structures in the world.

Since then it has welcomed nearly 15 million guests to its upper levels to dine, take part in a Sky Jump or Sky Walk or enjoy views up to 82 kilometres in any direction on a clear day.

To celebrate the birthday, Sky City is handing over the reins of the famed lights to the public for three nights.

On Thursday, Friday and Saturday members of the public can select one of eight colours to light the top of the tower for a special occasion, person, cause, or simply their favourite colour.

"From day one the Sky Tower's light shave held a special place in the hearts of Aucklanders, lighting to raise awareness for causes close to our hearts, in solidarity or in shared grief, to celebrate success, to support Kiwi teams, and for our diverse community", says John Mortensen, Sky City's Chief Operating Officer."

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This is an opportunity for the public to light for their special anniversary, proposal, or baby reveal, in support of their charitable cause or awareness day and to share that moment."

To be in with a chance of selecting your colour choice, head to the base of the tower on Thursday, Friday or Saturday between 6pm and 9pm.

The eight colour choices are orange, red, purple, blue, green, yellow, pink and a dynamic rainbow swirl. The colours will be selected on a touch screen and a second screen will show a livestream of the top of the SkyTower lighting in the colour.

As part of the birthday celebrations, New Zealand residents can also enjoy free entry on Thursday.