Bored with the luxury yacht? Personal submarines are a growing trend for the mega-rich.
Microsoft co-founder Paul Allen and Russian billionaire Roman Abramovich - owner of the world's largest private luxury yacht, Eclipse - are among those who have their own mini-sub.
Other ocean explorer types, such as British billionaire adventurer Sir Richard Branson and film director James Cameron, have custom-built subs.
In March last year, Cameron descended 11 kilometres into one of the ocean's deepest nooks, the Mariana Trench, in his Australian-designed solo sub, Deepsea Challenger.
Recreational subs could soon be jostling for space on board the world's luxury yachts, if latest design trends are any indication.
The first family-friendly five-seater has hit the market and could soon be vying to become the new must-have toy of the mega-rich.
The C-Explorer 5 was created by Dutch submarine maker U-Boat Worx to accommodate four passengers and a pilot, and has been dubbed "the world's first the subsea limousine".
This airconditioned mini-sub - which will set you back a couple of million - can descend to a depth of 300 metres, reach speeds of three knots underwater and stay below the surface for eight hours.
A range of larger recreational submarines that seat many more passengers are also on the market, but because of their size and price - in the tens of millions of dollars - they are mostly pitched at the luxury resort market.
The market for recreational mini-subs is relatively new, according to Barry Jenkins, chairman of Superyacht Australia, which represents businesses that sell products and services to the superyacht industry.
He says he spotted a mini-sub - a single-seater - for the first time at an international boat show about five years ago, then a double-seater appeared, and now the first five-seaters are arriving.
- Sydney Morning Herald