(CNN) — There’s been a trend in recent years for billionaire basements – subterranean extensions to the homes of the rich and famous, where they can bunker down and live large.

Now an Austrian company wants to extend this opportunity for deep-dive delights to the world of superyachts, by building customized private submersibles that can descend 250 meters (820 feet) beneath the ocean surface and remain submerged for up to four weeks.

Migaloo has revealed its ambitious plans for what it claims will be the “world’s one and only private submersible superyacht,” offering “a not-yet-existing alternative to large privately owned surface vessels.”

Billionaires’ playground

This submarine, named M5, would measure 165.8 meters in length and 23 meters across at its widest point, with a range of around 15,000 kilometers and a speed of up to 20 knots when surfaced (or 12 knots when underwater). However, says Migaloo, “The wished dimensions of the submarine-yacht hybrid, the exterior styling and the interior design are up to the owners’ preferences.”

So, like any billionaires’ superyacht worth its salt, the default design includes a helipad, a swimming pool and spa, a gym, art gallery cinema, party area with DJ booth, along with plenty of spaces to lounge or dine. Optional extras include a hot air balloon and underwater shark-feeding station.

There are also sub-tenders that can be specified, so up to 12 guests can set out on smaller submarines for more water-based antics.

‘Private submersible fortress’

“Owners are looking for privacy, security and protection for themselves, their guests and their valuables,” says CEO Christian Gumpold on Migaloo’s website. Customized security systems will be provided by US partner SAFE, promising “beyond military grade protection” for what it’s calling a “private submersible fortress.”

What’s the price tag on this private water wonderland? Well, there is no specific project price tag, due to all those juicy customization options, but the widely reported estimate for the Migaloo M5 is about $2 billion for starters (and that’s before you consider maintenance).

Submarine dreams

The M5 uses proven technologies borrowed from existing motor yachts and submersibles, such as double-hull construction and multiple pressure hulls, which helps on the safety and feasibility fronts. Although the question still remains as to who is deep-pocketed enough to buy this submersible Bond villain lair.

It’s not the first attempt to create a luxury submarine. Aston Martin revealed plans for a $4 million concept vessel in 2017. And it’s not the first time Migaloo has hit headlines for floating its extraordinary visions. At the Monaco Yacht Show in 2015, it showcased plans for Kokomo Ailand, its 80-meter-tall private floating island (with waterfall) that you can sail.

So will the Migaloo M5 concept vessel sail happily into reality or sink without a trace? It’s hard to say, but there’s probably some time to start saving your pennies.

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