Originally Posted by
dinanm3atl
Seems like outdoor ones are the real deal but they might not exist in Tokyo itself?
If bathing outdoors makes it real for you, you can find open air baths at some of the urban onsen (e.g. Oedo Monogatari / Spa LaQua) and in the more rural onsen. I don't know of a sento with an outdoor bath. That's not really a sento thing ...
Like me, Hailstorm sees some logic to the idea that sento is "real." Historically, sento were part of daily life for ordinary people. But these days ... Well, I'd be willing to bet that fewer Japanese people have visited a sento than have visited an onsen. So which one is more "real"?