[Letitring]

Okay. We know Montreal has a network of underground tunnels and passageways, complete with map posted on internet. good grief.

NYC-vast network of tunnels, same for NJ. Same thing for Chicago, same for Detroit. I'm going to check out Indiana and Ohio, next.

[mhking]

I'm going to check out Indiana and Ohio, next.

I don't know of any significant tunnels in Indiana outside the handful of caves near the Ohio River; likewise in Ohio.

You might want to check infiltration.org for other data.

http://www.infiltration.org/resources-ohio.html
http://www.infiltration.org/resources-indiana.html

[JustPiper]

What about caves in mountain states?

[mindspy]

What about our vast array of sewer systems? Rats do like to live in sewers.

[Oorang]

There are also a lot of underground tunnels on the west coast, back from the days of bringing in illegal Chinese and kidnapping drunks in the taverns to work on the boats. I know they are in Seattle, Portland and Pendleton (Oregon). The ones in Pendleton are a tourist attraction now. Probably are tunnels in San Francisco as well.