My Army Engineer SIL, who just retired, has for years been drawing an underground home, first for practice and then he became fascinated with the idea. One of the Northern (or MidWestern) Universities has an underground library that has a big hole in the middle for gatherings, and to let in light.
SIL wants a greenhouse on top to take advantage of heat rising and sunlight that would be gathered for power. Some of these places can have a herd of cattle grazing on top of it and no one inside would know it.
I'll bet now a lot of these will suddenly become popular.