[romanshrompsky]

I won't be able to back this up by any form of proof, but I have talked with the R&D departement of a major construction company located in France. They have plans to try to build underground cities in the foreseeable future in order to cope with 1) overpopulation in already dense cities and 2) provide alternative solutions to living in cities that are getting warmer and warmer. They showed me pictures of what it could look like, and you can basically imagine The Line in Saudi Arabia, but underground. That was 3 years ago.

What surprised me the most was that it was something they thought would be mostly sold to the very rich. This conversation got me very depressed.