The 173-metre tall mansion is called Antilia, after a mythical island in the Atlantic Ocean, and has just been completed after seven years of construction.

Owner Mukesh Ambani, his wife Nita and three children are set to move into the opulent 27-floor building after an housewarming party on October 28, which boosts a guest list of India's elite that reportedly includes Prime Minister Manmohan Singh and star cricketer Sachin Tendulkar.

The building soars high above Mumbai, giving its future residents a panoramic view of the country's financial capital, including its slums, and the Arabian Sea.

It was built to withstand military-grade explosions and an magnitude-8 earthquake, Indian media reported.

"I have seen several houses, including that of Lakshmi Mittal (an Indian steel tycoon and also one of the world's richest men)," a businessman, who was not named, told The Times of India.

"But Antilia is marvellous. I remember the house having a Picasso painting, it was one of its kind."

Mr Ambani, 53, is the world's fourth richest man and has a personal wealth of about $27 billion, but is set to become the world's richest in 2014, Forbes magazine estimated.

He is the chairman of Reliance Industries, India's largest private sector company, which has interests in oil, gas, textiles, retail and telecommunications. He also owns the Indian Premier League Twenty20 cricket team, the Mumbai Indians.

While the home cost about $77 million to build, Mumbai's growing property prices means Antilia is now estimated to be worth 15 times more - about $1 billion.

An Indian design magazine editor, Shiny Varghese, said Antilia was "so obscenely lavish" that she doubted many other wealthy folk would splash out in such a manner.

"But we are heading into the sort of culture where money is not a question when setting up a home," Mr Varghese told The Guardian.

Mr Ambani is believed to have previously avoided overt displays of his wealth, although Indian media reported his purchase of a $60 million Airbus corporate jet for his wife as a 44th birthday present in 2007.

"Perhaps he has been stung by his portrayal in the media as an introvert," Hamish McDonald, who has written a book about the family Mahabharata In Polyester, told the Guardian.

"Maybe he is making the point that he is a tycoon in his own right."

Mr Ambani and his family are reportedly currently living in the more modest surrounds of a 14-storey apartment building.

The specs

Antilia, dubbed the "mansion in the sky" by the Times, was built in consultation with US architecture firms Perkins and Will & Hirsch Bedner Associates.

Its construction was reportedly influenced by Vaastu, an ancient Indian belief similarly to the Chinese's Feng Shui.

Each level is twice as high as a normal floor.

No floors or rooms are the same, meaning the material used on one floor cannot be used in the construction of another level.

The first six floors are taken up by a car park that can hold up to 168 cars. The next floor is the lobby, with nine lifts servicing the building.

On the eight floor lies a 50-seat theatre. Another floor consists of a ballroom that has a ceiling mostly covered by crystal chandeliers.

Other floors contain a health spa with a gym and dance studio, swimming pools, lounges, a vehicle maintenance area and, of course, guest rooms.

The Ambani family will reside on the skyscraper's top four floors, which takes up about 37,000 square metres.

The competition

Mr Ambani's home is the world's most expensive, but he is not the only person to have built himself a luxurious abode.

The Villa La Leopolda, on the French Riviera, was built in 1902 by King Leopold II of Belgium. It was last valued to be worth at least $US524 million and is reportedly owned by a Russian billionaire.

Dracula's Castle, in Romania, was built in the 14th century and is now a tourist museum. It is perched on top of a 61-metre rock, overlooks the village of Bran and has about 60 rooms. It is valued at about $US135 million.

The Hearst mansion, also known as the Beverly House (not the Hearst Castle) in California, was valued at about $US165 million and has 29 bedrooms - but only three swimming pools. It is named after its former owner, newspaper baron William Randolph Hearst.

It is now on the market for $US95 million after its current landlord filed for bankruptcy.

The One Hyde Park penthouse, in London, has only six bedrooms but was sold for a cool £140 million ($226 million) in August. It has bulletproof windows, panic rooms and a numberplate-recognition security system for its car park.

Its owners will be guarded by security guards who were trained by the SAS and served by staff from its neighbour, the Mandarin Oriental hotel.

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