Underground housing, underground businesses, etc. Would that be better for the environment + possibly save on energy costs? Also possibly safer in certain scenarios like tornadoes etc.
Potential issues that immediately come to mind are ventilation, earthquakes, and flooding. But it’s not like underground dwellings/basements/etc. aren’t a thing, so maybe those issues have been addressed in ways I’m not familiar with.
For a single family dwelling (or any structure that isn’t too deep), reduced heating a cooling costs could make building underground cheaper in the long run.
For a large structure that goes deep, I doubt if it could ever be cheaper to building underground.