Matt Gross wrote about submarines for the super-rich:

• Luxury submarines – those that can travel independently and are able to regenerate power – start at $25 million.
• The most expensive is a $2.3 billion concept released by an Austrian design firm. It’s more submersible yacht than submarine, and includes a helipad, a swimming pool, and a dock for mini-boats.
• Owning a submarine is a little different than owning a yacht. There is the Pilot certification for one – which takes four months and involves training in an aviation style simulator.
• The submarines can go pretty much anywhere. The legal framework around traveling under the ocean is, well, murky.
• Countries like Greece are concerned that the rich will use the submarines to find and loot ancient ship ruins that could have historical significance.
• In addition to bragging rights, the mega-rich may like submarines because they finally give them a surefire way to avoid the paparazzi.

Read more on Bloomberg.