What exactly do you mean by "mysteries"? Things we don't yet know? There's only so many things that fall into that category, and most of those do so by technicality, since we have quality theories to begin with. You won't find that people write books about things we don't know- that forgoes the basic prerequisite for writing a good book. Our book list on the side bar has good general recommendations for the regions give mentioned. For the Americas, I'd recommend * Cities of the Ancient Andes,* Michael Coe's Mexico, and his The Maya. I myself am well versed in psuedo-archaeology and conspiracy theories, so I can give more specific recs on topics you're interested in but are frequently burdened with that rubbish: Nazca lines, Tiwanaku, Maya glyphs, etc.