Any recs for mysteries/thrillers/nonfiction with underground settings?  Either natural or man-made underground? 

I have "Journey to the Centre of the Earth," "The Mole People,"  (NYC tunnel dwellers) "Invisible Frontier," (exploring New York's underground), a few others, and am reading "Bad Blood" by Linda Fairstein,  fiction set in NYC water tunnels. 

I haven't the foggiest why I find these settings so fascinating...will be posting question to a few other groups too.

Thanks!

I read a weird book by Rex Stout called Under the Andes.  It's kind of a fantasy historical thriller about two brothers and an exotic femme fatale who have an adventure in a cave in the Andes.  Trying to get out of the cave, they run into a tribe of little people who have lived in the cave for centuries.  The tribe captures the woman and the brothers risk their lives to free her, and so on.  I read it one day when I was out of reading material (pre-PBS, of course) because it was online for free.   What goes on in the book is pretty outlandish, but I always like Stout's writing style and it was fun to read.

James Rollins has one called Subterranean. It's a very good book, takes place under Antarctica.  A bit of mystery, lots of thrills. It's one of his earlier novels and not as good as some newer ones, but he's very good. Might be worth looking into :)

The Manhattan Hunt Club by  John Saul was enjoyable. It's set in the underground tunnels of Manhattan.

I've also got a book called The Underground Man by Mick Jackson on my TBR list. I don't know if that one would meet your needs, but I've heard good things about it.

I may pop back in later because I know I read an older mystery a while back that was set in the Parisian catacombs, but I'll be darned if I can remember the name of it.

If you like Dosteyevsky (sp?) his book Notes from the Underground is a classic. There is a YA series that is based underground. The first book is City of Ember. 

Lost, by Michael Robotham is very, very good.  There are some very interesting sequences in the tunnels and caverns beneath London that sort of echo, to me,  what you are decribing.

On a cold London night, Detective Ruiz is fished out of the Thames with a bullet in his leg and no memory of the circumstances surrounding the shooting. In his pocket is a photograph of Mickey Carlyle, a seven-year-old girl kidnapped three years before and presumed dead. It’s anybody’s guess what Ruiz was up to–especially when a bloody boat discovered nearby makes it clear that Ruiz was not the sole casualty. But with Mickey’s killer convicted and behind bars, no one wants the case reopened. Ruiz’s only hope of unraveling the puzzle is to retrace his steps and re-create the night of the shooting. Under investigation by his colleagues and accused of faking amnesia, Ruiz turns to Joe O'Loughlin, hoping that the psychologist can help unlock his memory. Step by step, the pieces come together, revealing a twisted trail of grief, vengeance, and the search for redemption.