An archetypal Soviet-era garage box recently got converted to a Tiny House in Tartu, Estonia: https://g1.nh.ee/images/pix/iseloomuga-maja-muidu-paksude-ka...

Blocks of garages like these are a common part of Soviet heritage in Estonia, so they're essentially everywhere. Not quite sure, but due to its tiny size (probably ~215 sqft or ~20 m2) one may not need an extra building permit for doing something like ths.