Michael Murphy is helping luxury tourists sleep with the fishes.

The Auckland structural engineer, who has created world-famous public aquariums and underwater restaurants, has now designed the world's first underwater hotel villa, in the Maldives.

The two-level Muraka, which cost $22 million to make and is part of the Conrad Maldives Rangali Island resort, sleeps up to six adults and three children and can be hired from $73,000 a night.

The price gets you exclusive use of the resort's fleet of yachts and boats, 24-hour access to your own personal butler, housekeeper, security team and personal chef; seaplane return flights from from Malé, the capital; endless alcoholic and non-alcoholic beverages and daily spa and aromatherapy treatments.

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Guests can exchange glances with marine life including sharks and manta rays as they recline in bed five metres below the sea.

On the bottom floor, the king-sized bedroom, living room and bathroom have 180-degree views of the Indian Ocean through curved dome acrylic glass windows.

The top floor above the sea includes two bedrooms, butler's quarters, private security quarters, bar and dining area, living room and an infinity-edge pool.

Guests can descend to the underwater level down a spiral staircase or an elevator.

Murphy, whose global aquarium-design career began with Auckland's iconic Kelly Tarlton's, was the structural engineer and involved in the concept design.

"It's one of the most challenging projects I've had. And super exciting at the same time," Murphy said.

Murphy has his "fingers crossed" he may one day spend a night there.

With the undersea bathroom having full-length windows that look into the ocean, he jokes he "might shock the fishes".

Human privacy is assured, however, with the residence set apart from the rest of the resort.

Creating the underwater quarters was an engineering feat. The 610-tonne structure was built in three pieces in Singapore and assembled on a barge which was pushed-pulled by two tugs on a four-hour journey to meet a crane ship which took it to Rangali Island.

Two cranes on the ship guided the structure into the water and onto steel piles driven into the sea floor.

"That's the most fragile time, before you concrete them in. It's sitting there exposed," says Murphy, who helped oversee the operation.

Divers with microphones and underwater cameras liaised with the ship's captain, giving instructions to the crane drivers.

When the structure was connected to the piles, "everyone cheered".

The top level of was later connected to the spiral staircase leading down to the underwater quarters.

The two-year venture was the latest world headline-making project Murphy has helped design from his Manukau home office.

They include a massive shark tank at Palma Aquarium in Mallorca, Spain; a world's-widest acrylic tunnel (5m to allow two-way visitor flow) at Malaysia's National Science Centre aquarium in Kuala Lumpur; and a world-first 360-degree underwater acrylic tunnel (10m long) at Spain's San Sebastian Aquarium.

He also helped design underwater viewing windows for the penguin display tank at Christchurch's International Antarctic Centre, Auckland Zoo's sea lion pool, and the set of action TV series Hercules and Xena: Warrior Princess.

"I got approached by the film company, who were making a big pool with windows inside the tank so they could film battles in the water."

Murphy, who grew up in Weymouth, graduated with a Bachelor of Engineering in civil engineering at Auckland University in 1971.

He worked with consulting companies in New Zealand, South Africa and the UK on roads, bridges and industrial buildings, before setting up MJ Murphy Ltd in 1982.

He specialized in design in the coolstore/food processing industry.

In 1984, he was engaged to design and supervise construction of a 730-berth floating marina at Auckland's Westhaven Marina.

New Zealander Michael Murphy has designed a underwater hotel in the Maldives. Photo / Supplied
New Zealander Michael Murphy has designed a underwater hotel in the Maldives. Photo / Supplied

The floating marina, using big blocks of polystyrene with concrete sprayed around them to make floating pontoons – a concept based on an American system, was "pretty radical for its day".

The project led him to being asked to work on the creation of Kelly Tarlton's, for which he designed initial concept plans.

Following Kelly Tarlton's, he was contracted to do design work in aquariums around Australia and then the world, including Manly Underwater World in Sydney, Nanjing Underwater World in China and Sentosa Underwater World in Singapore.

The aquariums incorporated curved tunnels as a main drawcard.

"An arch is a much stronger natural shape, and it gives you a much greater feeling of immersion," says Murphy, who helped further develop acrylic arches which went around corners in a loop rather than only in a straight line as in earlier aquarium tunnels.

His pioneering expertise resulted in him being approached in 2004 to help design and supervise the revolutionary Ithaa (mother of pearl) underwater restaurant.

"Instead of fish in the tank, it was going to be people in the tank looking out at the fish and the coral.

"It was the first time we'd built anything in the sea. You wonder how to build it, how to sink it, how to transport it, before you even get around to designing it."

The Ithaa undersea restaurant designed by New Zealander Michael Murphy in the Maldive Islands. Photo / Supplied
The Ithaa undersea restaurant designed by New Zealander Michael Murphy in the Maldive Islands. Photo / Supplied

As with The Muraka, which means coral in Divehi (the local language), the Ithaa underwater restaurant was built in Singapore and shipped to the Maldives where it was sunk below the waves and secured to the seabed.

Calculations Murphy had to make for the project included checks of centres of gravity and flotation and stability in the water.

Constant dynamic forces had to be number-crunched not only for Ithaa's final position, but also during construction and its sinking.

To weigh it down so it was heavier than the amount of water it displaced, and not bob around or float away, they ended up filling it with 80 tonnes of sand – carried aboard in bags by a team of 50 men.

Murphy has since incorporated thick plate steel for that weight in The Muraka and on the Kiwi-built 5.8 undersea restaurant.

It is incorporated in the factory so no additional weight has to be added on site.

He was main designer and structural engineer for the 5.8 - the world's largest acrylic underwater restaurant - which opened in 2016 at Hurawalhi Island Resort in the Maldives.

Murphy has visited Ithaa, rated the most beautiful restaurant in the world by The Daily Meal website in 2014, several times.

"Before the diners go down to the restaurant, staff have a chat with them on the history of the place.

"On the occasions I've been there, they've introduced me to all the diners and said, we've got the actual designer here and talked about how it was built... it brings a tear to your eye."

Guests at the 5.8 (it sits 5.8m below sea level) are also told by staff of its New Zealand design and build team.

The 410-tonne Hurawalhi 5.8 restaurant was built in New Plymouth by Fitzroy Engineering and sailed to the Maldives on a 19-day journey.

Through his aquarium projects, Murphy has also been sought after to design life support systems for their marine occupants, from tropical fish to giant sharks.

"Probably one of the most complicated ones are jellyfish tanks, because jellyfish are so fragile.

"We design them with a circular motion in the tank to keep the jellyfish off the walls."

Designing the giant aquariums and underwater buildings requires a myriad of calculations.

Murphy says his life-long stuttering has motivated him "to prove yourself perhaps more than normally, because people might have a preconception".

But it also may have improved his mental arithmetic.

"Anyone with stuttering has a mental gymnastics going on in the back of the head. You say to yourself, I'm going to stutter on that word - what's another word that's similar that I can use as a subsitute."

He did see a funny side during the Manly Underwater World project when "three of the main players were on site one day and we all had stuttering problems".

"We were in a meeting with other staff there and we were all stuttering together and it was quite amusing."

At 70, Murphy is "hanging up my calculator", glad to "go out on a high" with The Muraka.

Although he is planning to watch movie Aquaman when it comes out in December.

A city under the sea, "that'd be a hell of a project!".