anyone know of any? I don't mean something kiddie, but something mature that doesn't involver death?

If you're willing to read short stories, about half of the Sherlock Holmes stories have no deaths. All four Sherlock Holmes novels are about murders, though.

I've read them already. I liked them but I'm just tired of crime, death mysteries.

I guess I was thinking something like lost but with more of a literal closure. Not interested in crime or death mysteries.

You want mysteries without any crimes? Maybe you ought to try histories of science and medicine.

The nature of the mystery novel pretty much by definition involves a crime of one sort or another -- with the mystery generally being how the crime is solved. The crime doesn't necessarily have to be a murder, although it often is. There are suspense novels that don't necessarily involve death, although it does pop up in most of them.

The No 1 Ladies Detective Agency is a series that focuses mostly on non-murder cases, although it's not a hard core mystery series.

You're likely familiar with Poe's Dupin "trilogy", but I have always enjoyed the short story "The Purloined Letter". Poe wrote three short stories featuring the main character Dupin - widely considered to be the first (or one of the first) fictional detective. The other two stories are worth reading as well, but they involve death and murder I suppose.

Poe emphasizes Dupin's "unique" abilities of keen observation and being able to think like the criminal. Most of Poe's stories can be enjoyed and interpreted in various ways and are much deeper than they initially appear to be. Come to think of it, I'd rather read these stories three times over than sit down with many of the modern mystery bestsellers, "The DaVinci Code" included. (Not that I minded "DVC", but I don't believe I thought about it once after finishing it.)

In reading this, I get the sense the OP isn't really looking for something in the mystery genre, per se. Instead they're looking for a story that has at its core a mystery - like the example given "Lost" (which features death and crimes, but the mystery aspect of the story isn't concerned with solving them).

There are a lot of movies like that come to mind - "Cube" and "The Village" for example But I'm having trouble thinking of books with that plot structure. Using "Lost" as an example of the type of stories the OP is looking for, I'm led to the sci-fi/fantasy genre. There must be good books that fit the bill, and I must've read some of them, but I'm drawing a blank right now. A lot of Dean Koontz books are centered around mysterious phenomena that the characters and readers are in the dark about to start (like Strangers, Phantoms, Lightning). Asimov's original Foundation Trilogy are centered around the solving of large mysteries (who is the Mule? what is Second Foundation?) The classic Ender's Game follows a group of individuals placed into a strange situation - and over the course of the novel, we gradually learn the truth about what is going on. The same thing for Farmer's Riverworld series - like Lost, we follow a large cast of characters thrust into a strange situation. And the drive of the series is for them to figure out what is really going on.

yes, thank you. I didn't express myself clearly in my op. I'll check out some of your recommendations. But yeah M. Night's movies qualify, or even things like memento or prestige. I can't think of many novels like that, but maybe because I just have not read enough.

The British writer Christoper Priest wrote The Prestige. Not necessarily for the casual/faint-hearted reader, if you read and enjoy The Prestige, several amongst his other works contain what could be regarded as integral "mysteries" or puzzles. Or maybe it's just [ahem] cognitive estrangement...

...It has been a while since I read them but, in particular, I'm thinking of The Glamour and The Separation.

If you want light-hearted mystery, I would suggest the Flavia De Luce series by Alan Bradley, about an 11-year-old girl in post-war England who solves crimes in her small town. Most of the charm comes from her narration -- she's a precocious genius who considers herself a brilliant and devious chemist, but she still has a weird and wonderfully childlike point-of-view.

The first one is called The Sweetness at the Bottom of the Pie. There are two more thus far. The first two feature dead bodies but they certainly aren't focused on death and mayhem -- Flavia simply works to solve the cases.