[someremains]

I explored this in 2002 with a group of friends while on Christmas break from school. We had to slide down the side of I-75, pry open a grate and drop down onto the top of the water mains running through. We walked almost the entire length of the system before popping out of a manhole in the middle of down town Cinci. The stations and tunnels seem to have been used as some sort of shelters during cold war as there was large amounts of "artifacts" left over from the Civil Defense era (water canisters, beds, etc.). A great experience.

[keithpeter]

In some UK cities, they build hardened telephone exchanges in the late 50s early 60s to try to guarantee communications in the event of a nuclear war. The one in Birmingham is now used for data cables and isn't open to public because of water-table rises.

http://www.subbrit.org.uk/rsg/sites/b/birmingham_anchor_exch...

http://www.birminghampost.co.uk/lifestyle/birminghams-hidden...

The Anchor exchange construction project had a cover story: an underground for Birmingham that, alas, had to be cancelled later because of changes in the market!

The main one in London was re-purposed from an abandoned underground station, itself used as a communication centre in the 2nd world war.

http://www.subbrit.org.uk/rsg/sites/k/kingsway/

So a civil defence use for such tunnels sounds very plausible. No budget line, no need for any questions &c.

[noer]

There's a building in lower manhattan that was designed for that purpose as well: https://en.wikipedia.org/wiki/33_Thomas_Street Technically there are two buildings built for telephone switching, but I don't think the other building (375 Pearl St) is nearly as overbuilt.

[petepete]

Here are some pictures of Oldham's nuclear bunker. And no, I have no idea why it was deemed necessary to build one in Oldham.

http://www.manchestereveningnews.co.uk/news/greater-manchest...

[Graham24]

The block of flats I live in used to be a UK telephone exchange, and it has some seriously thick concrete walls and massive steel girders. I dare say this was partly to house the old electro-mechanical exchanges, but it does look like it'd survive a bomb blast.

[Yhippa]

You have just given me a very good reason to visit Cincinnati.