Outside of Sailes-de-Bearn, France, René Douma, and his mother, Marianne built two houses into the hillside on the family farm using only books and online forums for reference. Despite their lack of experience, the twin homes are breathtaking and have surprising custom details.
The video dives deeper into why the Doumas took on this challenge, how they decorated the interiors, and the various materials they used, including covering the homes with dirt so the native grasses would grow back.
Source: https://twistedsifter.com/videos/family-builds-twin-underground-homes-on-ancient-farm/