As if being a small island nation wasn’t enough, 73 percent of Japan’s land is occupied by uninhabitable mountainous regions. So flat land obviously comes at a premium. But one architect has now gone where others have tended to shy away: into the sloping side of a mountain.

Completed in 2015, Greendo is an undulating, seven-unit residential building that’s been carefully inserted into the side of a mountain in a town in Takamatsu City, located in Kagawa Prefecture on the island of Shikoku.