Real-life dungeons

[thorr-kan]

Wabasha St. Caves, St. Paul, MN:
http://www.wabashastreetcaves.com/
Former speakeasy and Prohibition smuggling site, now a restaurant and event location.

There's a restaurant in Stillwater, MN with dining rooms in the limestone caves of the hillside. Used to be/may still be a winery. Lunarossa Wine Bar is the name I turn up, but not the one I remember. Location's right though, so probably a management change:
http://lunarossawinebar.com/cave-tours-events-2/

Urban salt mines in general, Detroit, MI in particular:
http://gizmodo.com/the-incredible-ur...r-f-1516664767

Poland's got a number of salt mines that have served as religious sites over the years:
http://www.cnn.com/2013/11/11/travel...unesco-poland/

[Daigoro]

White Cliffs, NSW, Australia, is too far out of the way and too underpopulated for much interesting to happen there, but the idea could be transplanted to a fantasy setting or somesuch.

It's a warren of hand cut opal mines. Many have been abandoned and have little more than a sign board warning against a 100 foot plummet, while others are like hobbit holes- the first 100 foot or so after the entrance is now the miner's domicile, with separate kitchen, living room, dining room, bedrooms, workshops and such, but continue further in and it becomes an active family run opal mine which goes some distance into the hillside and down numerous levels.

Google Images
Another Google Images
Wikipedia

[quarkstomper]

A couple months ago I heard a story on NPR about a beer baron who had built his brewery over a network of caves because, in the days before reliable refrigeration, the caves were the most practical way to get the lower temperatures needed for the brewing process. A part of the cave system extended under his mansion, and he built a little salon in it complete with a theater, to entertain guests in the summer.

Now I'm blanking on the name. But I can't help but wonder if he might have been Thomas Wayne's grandfather...

[Anaraxes]

Originally Posted by quarkstomper

built his brewery over a network of caves

Quite common for wineries in California, even recent ones. The more natural climate control you have, the less you'll spend on keeping the temperature where you want it.

http://www.winecountrywelcome.com/winecaves.php

[patchwork]

The 1906 earthquake in San Francisco slammed the old waterfront down and folded what used to be seabed over it in an instant. If you know where to get down and don't mind going somewhere that isn't even slightly structurally sound, you can walk along the eerily preserved 1906 Market Street, still down there...

[(E)]

Old Maori burial caves turned into wine cellars in Whangarei NZ. (not a system of caves unfortunately but fiction can fix that)