So to answer your original question, they're big in Europe. Poland and Germany, mostly.
The wikipedia article on them must be outdated as fuck because it says they exist only in Japan and there's one in Warsaw. It made no mention of Heathrow Airport or Germany.
It looks more like when you go to the pound and see all the animals locked upYou think I'm here for your fucking entertainment?
I Google Imaged "capsule hotels" and I got this:
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The wikipedia article on them must be outdated as fuck because it says they exist only in Japan and there's one in Warsaw. It made no mention of Heathrow Airport or Germany.