Q:  What is a capsule hotel? A:  A capsule hotel is popular among businessmen in Japan.  Often times they work late and miss the last train home; therefore, needing a quick, quiet, inexpensive hotel with all the necessities.  Enter capsule hotel.  You literally sleep in a "capsule."  The one I stayed in was two levels high (luckily I was on the bottom), but I think some go three high.  It was hard finding a capsule hotel to stay in because most are just for men.  However, in Osaka I found one with a women's dormitory as well.Everyone is given a key to enter their area:  men or women's.  In your area there is a locker room, public bath spa, laundry facilities, and the dormitory rooms of capsules.
They give you pajamas and you can even buy business-type clothing for men upstairs.  Everything you need...
Here are some pictures of inside the capsule. 

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