What is something that is impossible to make, but if it were possible, would benefit a city?

Question

What is something that is impossible to make, but if it were possible, would benefit a city?

Answer 1

If it were possible I would make all the major cities untouchable by bombs, warfare, any kind of killing agents. It would have like a beam surrounding the whole city so it would entirely safe from anything harmful or destructible.

Answer 2

environment!

city hall?

Answer 3

two cities really one on this coast one on the other.a big conveyer belt that not only created energy but transported people to and from.but this could probly really work.but people are so greedy that it would never happen.to much displace ment to much land to buy and a hole lot of work.which you will not get out of the public market today because we have gotten so lazy.but this is what we need is something exstavigantly big or unique to get us back together again.just like hoover dam.