One of the places with the largest number of narrow buildings in Tokyo is Ueno, the heart of the old Shitamachi. During the Edo period, this area was inhabited by people considered at the time “lower status classes", like merchants and craftsmen. The building spaces were very narrow and since many buildings have been passed on from generation to generation, there’s no wonder that there are so many “pencil-buildings” in this neighborhood.

Here is one of my favorite narrow buildings, located in Ueno Matsugaya. I like it because it has a very particular architecture - just look at the window from the top floor.
Regarding its width, look at the nearby bicycles for comparison…

Narrow Buildings, Ueno Matsugaya, Tokyo

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Yesterday’s Japan Photo: Atsuta, the Second-most Venerable Shrine in Japan