Since it's cheap, mainly business men who couldn't go home stay at capsule hotels. Also, capsule hotels are popular among foreign travelers. In capsule hotels, each guest stays in a small sleeping space (capsule) which is about 3 feet by 4 feet by 6 feet. In a capsule, there are a TV, an alarm clock, a light, and so on. The open side of a capsule is shut by a curtain or a screen, and it is unlocked. To sleep well in capsule hotels, earplugs might be helpful.
Women are sometimes not allowed in capsule hotels due to security reasons. But nowadays there are capsule hotels offering seperate floors or areas for male and female guests.