While the absolute world record goes to this Polish home/art installation, Japan is the king of ultra-thin houses, with these sometimes futuristic sometimes traditional structures popping everywhere. Its architects are masters in the use of space, so their slim homes look beautiful outside and comfortable inside. I wish NYC and other megalopolis had the same standards.
https://gizmodo.com/the-slimmest-houses-on-earth-are-made-in-japan-5107283
Instead, in Manhattan and Brooklyn they just make shitty tiny 1-bedroom apartments in shitty buildings made of shitty prefab walls for $4000 a month.
https://kotaku.com/cramped-or-not-i-want-to-live-in-these-tiny-japanese-h-1051646360