Chelsea sugar factory will be opening its doors to the public again.

After two decades, Auckland's landmark Chelsea Sugar Factory is opening its doors again, allowing to see the famed "sugar mountain".

Since tours of the sugar works stopped in the 1990s, people have seen the "distinctive" pink building and wondered what was happening behind the closed doors, Bernard Duignan, general manager New Zealand Sugar Company, says.

"This is us saying 'come and have a look, we're happy to show you'," Duignan said.

The Chelsea Sugar Factory has been on its original site near the harbour bridge in Birkenhead since 1882 and today much of the factory building is still the same as when it was built 134 years ago.

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But, in the past year, construction of the Chelsea Bay Visitor and Food Education Centre has added a new, modern, dimension to the heritage site.

Chris Skelton/STUFF New Zealand Sugar Company general manager Bernard Duignan, and visitor centre manager Ginny Brocklehurst at the Chelsea sugar factory which is opening its doors to the public again.

NZ Sugar Company had invested $7 million into a new visitor centre, which is open to the public from October 27.

Existing buildings, including the factory which was made from one million hand-made bricks in the 'pink-orange' paint colour called Tuscan Red, sit alongside the new "contemporary industrial" style visitor centre.

The glass-fronted cafe, Sugar at Chelsea Bay Bakery and Eatery, and the visitor centre which hosts an interactive zone, including a digital baking challenge with renowned New Zealand baker Annabelle White, is free entry and is open seven days a week.

CHRIS SKELTON/STUFF Bernard Duignan and Ginny Brocklehurst at the new interactive zone in the Chelsea Bay visitors centre

The new Edmonds Baking School currently caters to school children, but adult baking classes would be coming in the new year and will have a fee attached.

Duignan estimated Chelsea Bay would be visited by more than 60,000 people in its first next year.

"It is a bit of a destination that we are creating," he says.

CHRIS SKELTON/STUFF New Zealand Sugar Company general manager Bernard Duignan at the 'sugar mountain', which is subsequently washed.

"Chelsea Bay is the culmination of more than 10 years of planning and development, and we're very excited to finally be able to open our doors to the public.

"You get to see a live food factory and you can't do that anywhere else.

"We recognise that as the only sugar manufacturer in New Zealand, we are in a unique position to be able to show people what's involved in the production of our ingredients, and also celebrate the tradition of baking that has helped define us as New Zealanders."

The Chelsea Sugar Factory is a processing plant, which receives raw sugar shipped into the Waitematā Harbour to convert into the brand's iconic pantry products.

In the 1980s and 90s, tours of the factory would draw around 10,000 adults and children each year.

After a 20-year hiatus, weekday tours of the factory resume this month.

The walking tours of yesteryear have been replaced by a re-designed hour-long train ride tour that takes visitors through the fully operational factory to see how raw sugar makes its way from being offloaded from the ships berthed at the deep-water port and turned into the finished products.

The sugar arrives by ship every six weeks and comes from the tropical climes of Queensland in Australia, or central or south America.

First stop for the raw sugar once it arrives in Birkenhead is the raw store room, which can hold 40,000 tonnes of raw sugar crystals in a space approximately the size of two rugby fields, and this is where the famous 'sugar mountain' is formed.

Once you move on to the factory stage of the tour, a warm, sweet smell hits the senses.

Chelsea Sugar refines more than 200,000 tonnes of raw sugar each year for both domestic and international consumption and Chelsea Bay manager Ginny Brocklehurst says, for some people, seeing the process of how sugar ends up in the supermarket can be eye-opening.

"In the interactive area we show the process of it and particularly the kids see it as sugar cane and say 'did it really start like that'.

Surrounding the factory and visitors centre is Chelsea Estate Heritage Park which was sold to Auckland Council in 2008.

Duignan and Brocklehurst encourage visitors, including dogs on a leash, to explore the grounds and take in the views back across to Auckland city from what they hope will once again become a popular spot with locals as well as international visitors.