The Capsule Hotel, also in the Netherlands, has its guests sleep within bright-orange, 133-square-foot oil-rig survivor pods moored in the Hague.

FORBES: The World's Tiniest Hotel Rooms

Shimizu wondered if he might combine the best points of a capsule hotel - price and convenience - with the gentle touches of a traditional ryokan.

BBC: Capsule Ryokan Kyoto, where modern meets traditional

So perhaps it was only a matter of time before someone decided to combine the two quintessentially Japanese forms of accommodation: the traditional Japanese inn, or ryokan, and the capsule hotel.

BBC: Capsule Ryokan Kyoto, where modern meets traditional