[jackchun]

for underground city, the air are likely toxic and dangerous to our health, only fresh air exists in normal city areas, except nuclear wars or accidents happen

[OldGuy]

I would never consider moving to such a place. It would be hell on earth. No man made environment could ever compete with all that nature has to offer. Even if there was a disaster that called for everyone to move to shelters, I would prefer to remain outside and die to avoid such a place.

[Netherrealmer]

for underground city, the air are likely toxic and dangerous to our health, only fresh air exists in normal city areas, except nuclear wars or accidents happen

Finland have no air pollution though, It is one of the cleanest countries and its transitioning to oil free.

[Angie10]

Wow, interesting! Maybe that's the route down which other countries will now go not just in case of some sort of attack, but because we're running out of space.

[Netherrealmer]

Wow, interesting! Maybe that's the route down which other countries will now go not just in case of some sort of attack, but because we're running out of space.

Countries with volcanoes and have regular earthquakes won't be able to do it.

[Ourella]

Oh no! Underground cities look horrifying for me. Nothing could replace real sunny spells, light, stars, noise, insects. The real environment is spectacular. I even did not manage to live on the 7th floor. For me, it was disastrous not to see the real earth under my feet.

[Netherrealmer]

Oh no! Underground cities look horrifying for me. Nothing could replace real sunny spells, light, stars, noise, insects. The real environment is spectacular. I even did not manage to live on the 7th floor. For me, it was disastrous not to see the real earth under my feet.

Would you consider being a tourist in one of them somehow? a temporary visit is different from living in them.