[Nyororin]

On western television they love to hunt down the tiniest ones, and pretend that they are ever smaller by having some 6'5" guy crawl halfway in and let his legs stick out...

In reality - the majority are quite long and spacious. And they`re certainly not the main attraction. Think of it as like a private bed in a resort hotel. The whole facility is open for use. They almost always have extensive baths, massage facilities, huge relaxation rooms with private theaters, gaming arcades, gyms, etc.
All of it is included in the price. You can also use the facilities without staying overnight for about 1000yen less.