It would be like a giant undergound city with sectors and everything. It could connect to other parts of the country (Capital Wasteland/Mojave Wasteland/North/Etc) through a railway system, but yeah I thought that this would be awesome to show a lot of people working together. Of course having it connect to many other parts of the country would be one hell of a task to pull off i wonder if Bethesda could do it...oh yeah bring back Desmond that Great Game plot was awesome.

http://www.youtube.com/watch?v=R6Mj1Us13Yk&feature=related

Have to agree with Styles here.

It's not a good idea at all.

One, there isn't anywhere near enough people capable of working together to achieve such a thing.

Two, the tech no longer exists (if it ever existed) in the Fallout world for hollowing out huge underground caverns and drilling massive interconnecting tunnels. If it did, it wouldn't work anymore. If it worked, no one would no how to use it. If someone knew how to use it, why would they drill a tunnel to a place they've probably never heard of?

Three, why?

We have the technology to build the tunnels at least.
http://fallout.wikia.com/wiki/Find_the_excavator_chip

What is probably missing though is the practical geological survey skills. IANAG but not all ground is the same, some is soft and squishy and some is hard as a preverbial rock. Some bits are hard to dig through, some bits are silly to dig through as they'll collapse or let in water.

But I agree with the rest - it doesnt make a lot of sense; why would people build an underground railroad when there are many more pressing matters, and if a transport network is required in a somewhat civilised area, it can be done a lot cheaper and easier on the surface. You tend to go underground where going overland is Geographicly difficult (Very Steep hills and mountains, Urban Areas, The English Channel) enough that the surface becomes unfeasable.

The rest of the OP kinda sounds like Fallout 3, except more of it....

I don't think that we would have ever needed the vaults in Fallout universe, if the post war people could build something like that...

Anyone else think 'Mega-City 1' when they saw the title? Man, I'd love to see a sandbox-style Judge Dredd game.

We have an http://www.gamesas.com/index.php?/topic/1175896-official-future-fallout-locations-suggestion-topic-5/ for Fallout 4 location suggestions, you're welcome to repost this in there.